Response of Various Extrusion Parameters to Different Outputs: Review

: Extrusion as a process involves the introduction of compressive force to drive metal sample out of the die in order to subject it to plastic deformation which in turn will enhance both mechanical and metallurgical properties of aluminum. One input parameter can as well impact other parameters of extrusion. The extent of mechanical properties improvement and effects on other factors depends on adequate selection of the process (input) parameters. The interaction of these parameters influenced the responses (output parameters) in different way. Therefore, this review paper focused on extrusion processes, different extrusion input and responses and related work by different researchers on how different extrusion parameters influences different responses


Introduction
Extrusion describes a forming technique whereby plastics or metals are compelled through a die or die series, leading to a particular uniform cross-sectional shape [1].Extrusions can be tapered or stepped with the appropriate tooling.Extrusions may either be thick or thin, rigid, or hollow cross-sectionally.The extruded billet, which may be 30.5 m long or larger, is then trimmed to suitable stock size and used for further manufacturing as individual items, parts for production, or as raw stock material.The depth of the extrusion is represented as a circle dimension, which corresponds to the shortest circular diameter that may enclose the cross-section of an extrusion.There are two ways of designating the extrusion process [2].*Corresponding author: Azeeztemitayo221@abuad.edu.ngOne, extrusion based on operating temperature which may extrude hot or cold.Two, extrusion based on direction of ram movement which could be a forward or a backward extrusion.

Direct / forward extrusion process
This refers to the commonest extrusion styles [3].The extrusion cycle starts with a billet of aluminum which may be softened through heating before extrusion [4].The heated billet is put in the press of extrusion, a sophisticated hydraulic instrument in which a ram pushes a dummy block, forcing the softened metal to produce the desired shape via an accurate opening referred to as a die.This method could be used for the development of an open or closed-end tube.The bottom of the closed-end tube is equivalent to or thicker than the side walls.Side walls can be either tapered or parallel.The advantage of forward extrusion is the possibility of achieving a closed tolerance.The shape of the extruded product will be identical to that of the die channel in this method.The key drawback of this procedure is that opposed to the indirect approach, high extrusion force is needed and lubricants are used to minimize the friction effect, destroy equipment and make the operation fast.Figure1a displays a standard forward or direct extrusion image.

Indirect or backward extrusion process
In this phase, the die is enclosed inside the hollow ram, which travels from one end of the stationary billet to the other, causing the metal to flow through the ram, taking on the die form as it does [5].The actual process of extrusion begins with the ram applying pressure to the billet inside the enclosure (Figure 1b).The benefit of indirect extrusion is that the friction in the billet is minimized, which tends to improve the pace and performance of the made products.No heat is generated in the cycle because of friction, and thus the extruded component does not crack and the unit becomes less wear and tear.
Different hydraulic press designs can exert pressure ranging from 100 to 15,000 tons anywhere [6].The press pressure function dictates how big it will create deformation.The size of the extrusion is calculated by its largest cross-sectional axis, also called its position inside a circumcising circle diameter [7].When friction is first exerted, the billet is compressed against the die, getting narrower and broader until complete touch with the walls of its container limits its expansion.Then, as the friction rises, the porous (remain solid) metal has no other way to go and starts pressing through the die's developed orifice to emerge as a completely formed extrusion or profile on the other side.Approximately 10% of the billet, including its outer skin, remains in the container [8].The finished extrusion is chopped off at the die and the product left is collected for recycling.The still-hot extrusions are often quenched, mechanically processed and aged after it leaves the die.Figure 1b shows a typical expression of the reverse extrusion process.

Hot extrusion process
This process utilizes a billet which varies from 90 °C to 1260 °C [11].Aluminum is the most often used hot extruded material, with billet temperatures ranging from 300°C to 600°C.This operation is frequently carried out at substantially greater temperatures than the recrystallization temperature of the component to be extruded.The heated billet is enclosed within a container, force is applied, and the billet is extruded by a die or dies.Hot extrusion is employed to produce near-tolerance measurements as well as flawless, smooth surfaces.Even so, the procedure is very cheap, so much of the extruded metal is functional.The major aspect of hot extrusion is the forward or direct type [12].

Cold extrusion process
This, on the other hand, is the method of extrusion of a billet at its initial temperature and, in certain situations, in cold extrusion, we have a dry and lubricated form, where the dry extrusion is one in which no lubricant is used, and the lubricant kind is used where lubricants are applied to the billet and container surfaces to minimize the highpressure one that accompanies the procedure [12].
In order to conduct the extrusion operation, it is important to make several components or accessories available, such as; i.
Billet: This is a metal log that is machined in many different diameters and cut to different lengths.The billet is heated to a plastic condition and hydraulically pushed through the die to achieve the required form.Figure 2a displays a cylindrical billet.ii.
Punch: It is constructed of a high wear-resistant material that is specifically used to move metal out of the die.Figure 2b displays the standard depiction of a punch.iii.
Die: These are components that are constructed with a channel and are also made of high resistance to wear.The extreme pressure of the punch is used to force the metal out of the desired shape.Figure 2c displays a typical depiction of an ECAE die with a cylindrical channel.iv.
Hydraulic Press: This is the device that delivers the appropriate force for the extrusion to occur.The Hydraulic Press must concentrate its energy on the punch and push the billet out of the die.Figure 2d displays the hydraulic press illustration.v.
Furnace: It is used to heat the metal to the recrystallization point, although not to the melting point.

Various extrusion inputs
Extrusion inputs such as billet homogenization, billet preheating, extrusion pace, press quenching intensity, size effect, die configuration, die power, specimen range, friction state, temperature state and other boundary conditions influence the characteristics and nature of deformed items.The set of parameters influencing the properties and reliability of the material studied by many researchers is further addressed.

Billet homogenization by multiple extrusion passes
Multiple extrusion passes have been proposed as one of the measures to ensure adequate homogenization.The intent of multiple pass numbers in the ECAE method process is to homogenize and lessen the micro-segregation of magnesium and silicon across the framework.Second, the transformation of the insoluble eutectic phases into the AlFeSi balance phase.This generates a high as well as uniform hardness and tensile strength aluminum alloy.Zhang et al. (2015) suggested that the excessive or inadequate accumulation of Mg and Si in aluminum alloys induced by the nonuniform (non-homogenized) distribution of Mg and Si in solid solution before artificial aging resulted in low strength in the equal channel angular extrusion.

Pre-heating of billets
The main objective of pre-heating is to reduce alloy stress flow [18].This enables extrusion at maximum velocity, simultaneously maintaining surface quality and mechanical properties.The preheating rate is based on duration, to improve the billet's post-homogenized microstructure.It has been revealed that extrusion ability, along with mechanical characteristics as well as surface finish, could be enhanced greatly by the use of billet preheating techniques that deviate from established standard production systems.Any Mg2Si phase that exists in the homogenized framework has ample time during the heat-up phase to reestablish a solid solution [18].The amount of Mg2Si dissolved is affected by the pre-heating level.More Mg2Si may return to the solution as a result of gas-fired re-heating.[18].

Extrusion speed and temperature
During extrusion, the process factors (input factors) such as speed and temperature enable the aluminum and its alloy to dissolve, resulting in an adequate microstructure for press quenching and ageing process [19].The exit temperature changes with the extrusion because its variation depends upon the preheating temperature of the billet and the speed of extrusion due to the transfer of heat from the ticket to the container and the heat produced by deformation and friction.The boundary diagram (Figure 3) illustrating the interconnectedness between exit speed and billet temperature [20].Limit curve 1 indicates that at any point, the surface temperature cannot exceed the maximum value, resulting in excessive scoring or transverse cracks.According to Limit Curve 2, the average temperature of the segment must be sufficient to ensure that the heat treatment solution is sufficient for an effective heat management system using Al-Mg-Si alloys.Limit curve 3 shows that the press and its power source define the overall extrusion load and ram speed.When the billet temperature is between 380 and 400 o C, the extrusion speed is limited to 40-50 m/min.In the case of 6063 aluminum and its derivative 6060, the deformation temperature should be between 500-600 o C, for 1% Mg2Si (by weight), as shown in Figure 4. Therefore, if the amount of Mg2Si in 6060 alloys is less than 1%, the deformation temperature must be within the range.As aluminum deforms at high temperatures, there is a slow development and emergence of a microscopic grain structure [18].Several hot worked alloy compositions, particularly those of stronger alloys, can, nevertheless, withstand the recrystallization whilst exposed to heat treatment solutions [22].The massive recrystallized grains can be placed right beneath the extrusion's edge.The deformation during extrusion is more severe on the outside surface than in the center.Higher than usual extrusion speeds and lowest billet temperatures might led to a completely recrystallized morphology with a fine homogeneous particle size for weaker alloys like AA6063 or most medium-strength alloys [23].Nick and Chris (2012), in AAA 6065, examined the billet temperature and ram speed impact on grain structures as presented in Figure 5 [23].It demonstrates that the dashed line in Figure 5 indicates that the Mg2Si particles are sufficiently dissolved to meet the T6 property standards at an actual temperature of 510 o C. T6's yield strength is determined by any events that occur on or through the right side of this dotted line.Reduced workpiece temperatures and rapid ram speeds, as well as a finer grain scale, enhance this situation.On the other hand, increased billet temperatures and low ram speeds facilitate the durability of the un-recrystallized material, so when recrystallization happens, the grain size usually becomes smaller.
A constant temperature of exit during the extrusion process is needed to achieve standardized product quality [24].The extrudate's extrusion temperature varies from stage to stage and along its length in relation to the ram position in the course of extrusion.The original temperature of the billet and container as well as ram speed shall be suitably allocated for equalization of the billet to container flow and the generation of heat generation as a result of shearing deformation.Figure 6 depicts the steady production temperature obtained [25], based on experimental AA6060 (dark line) extrusion at a velocity of ram 2.0 cm/s, with an extrusion ratio of 10:1.This indicates that if the extrusion variables are appropriately chosen and the extrusion speed is controlled as needed, a reliable temperature response may be attained.

Die effect
Strong surface finishing dies and mechanical properties are employed to preserve them from wear and tear [26] in micro-forming operations.Materials for die production were developed and utilized with the high stress, oxidation and thermal shock resistance.According to Adeosun et al. (2014), in both tool steel (TS) and plain carbon steel (PCS) dies, the needed pressure in extrusion of Al-6063 alloys rose with an increase in die angle, although the pressure needed for TS dies was larger at the die with less angle [27].

Ultrasonic vibration effects
Micro-extrusion has been vibrated, mostly to improve its ability to shape and the roughness of the product's surface.Figure 7a and b show how ultrasonic vibration is employed in the extrusion of Al-1100 to reduce flow stress and friction coefficient between the die and work-piece surfaces.Bunget and Ngaile (2011) investigated micro-forward and dual cup extrusion and discovered a constant decrease in the micro-gap between die and billet, resulting in an extrusion load reduction requirements and surface roughness, as shown in Figures 7a and b. Figure 7a further shows that the ultrasonic vibration lubricant Lubsol W-72 SK has an 18% lower punch load reduction ability than the Lubsol W-72 SK with no ultrasonic vibration.LubsolW-72 SK lubricant performed better (18%) than polymeric lubricant (16%) and Dailube DR-38 lubricant (12%) in terms of load reduction [28].surface finish [28]

Friction effect
Lubricants are employed in friction reduction between the die and billet, which further lessens the required material deformation load.Friction factor reduction relies on the lubricant's form employed, the work-piece and die geometry, as well as the operating condition.The friction factor is determined by the type of lubricant used, whether it is liquid, solid or dried, and its composition [29].The friction variable is classified into closed or open lubricant types based on a mechanical-theoretical concept.
There is a decrease in friction when less viscous organic lubricant is applied to the soap during the cold formation of steel (Flitta and Sheppard, 2003).Refined extrusion palm oil lessens the load relative to additive-free paraffin organic oil with better surface structure [31].
The role of lubricants cannot be ignored for their part in forming processes, because these procedures cannot be performed effectively without suitable lubricants.
Lubricants are generally present in liquid or gaseous form and are applied to the working surface to facilitate smooth billet extrusion and to limit the danger of folding, which usually occurs in deposits in the container's dead region.These impact extrusions in several ways, especially as they function as heat removers [32].It also helps in eliminating flaws like internal pipping of the thin billet layer, which is extruded onto the extruded rod.Adequate lubrication increases the life span of forging dies.This is especially necessary for the forging of aluminium, magnesium and stainless steel, which appear to cling to the dies [33].Syahrullail et al. (2011), discovered that increased lubricant viscosity of the specimen reduces material-to material interaction, which improves sliding velocity.For the extrusion of 21B3 steel that has been annealed, the friction coefficient with the application of vegetable oil (VO) is comparatively greater than that of other lubricants such as extreme pressure oil (EPO) with sulphur compounds, cutting oil (CO) and new extreme pressure oil (NEPO) as analyzed in Figure 8 [34].The coefficient of friction can be reduced by the application of an appropriate lubricant.However, increased temperatures and pressure nullify the effect of lubrication.More study is thus required to test alternative commercially available lubricants under varied extrusion conditions [31].Engel (2006), has established that the open lubricant may have two main effects on friction impact, in which the part of the open lubricant packet together with friction factor rises with the reduced sample size, whereas in the event of a close lubricant, the hydrostatic pressure created in the tight lubricant packing region reduces the stress of the packet working on the roughness regions [35].
According to the improved Tabor model and as indicated in Equation 1, the coefficient of friction (μ) during extrusion is a function of the friction factor (f), strain hardening constant (n), and contact area ratio () [36].This formulation is necessary to forecast μ for various grain sizes during the miniaturization process.Two different laws of friction scenarios described in Equations 2 and 3 are utilized to assess the influence of stress and deformation behavior in the elastoplastic ranges, focusing on Coulomb and continuous shear stress [37].As a result of the size factor, surface waviness variance in the elastoplastic regions may lead to various frictional stresses (.)An increase in load supplied through the punch can be forecasted where the frictional force is denoted by   ,   force, Δ denotes normal stress, A is the area in contact,   is the frictional shear factor (0-1) while Ks is the shear yield strength.Equations 1 -3 will be assisting in building the suitable configuration of die to maintain load during deformation.during extrusion [34].
During the micro-extrusion process, it was further discovered that for a reduction in the coarseness of the samples, the frequency of the surface wave fluctuation increases, leading to a rise in the coefficient of friction as seen in Equation 4but high wave frequency fluctuations with an increase in the extrusion pressure are not accurate for  9 indicates that a the friction coefficient increases the load and falls with an increase in the billet original temperature [38].
Lubrication often impacts the flow of metal in the cavity of the die as it decreases friction between the die surfaces and the forging.Hot metalworking lubricants typically contain a solid, inert substance such as graphite in a car and mineral oil.The carrier burns or evaporates at forging and extrusion temperatures, but is left with a film of solid lubricant [39].Graphite coatings can be difficult to extract from aluminum and magnesium, but they may not pose any issues for steel and other nonferrous alloys.Graphite, talc, chalk, lime, mica and bentonite are popular fillers for lubricants in metalworking.

Temperature/ Heat effect
The micro-extrusion heat generation is less than the conventional extrusion heat generation [36].Saotome and Inoue (1994), discovered that the dissipation of heat in UFGs rose with an increment in speed of extrusion relative to CGs. during cold extrusion declines with decrease specimen size (Figure 10).The curve representing the Stress strain behavior for (a) different sizes of grain at 0.2 mm uniform thickness and (b) uniform size , different thicknesses and subjecting it to hot extrusion, the tensile strength reduces with a decrease in size of grain [40].Tensile strength was measured at various ARLPSO (aspect ratio of long-period stacking order), metal rate of flow, strains and temperature settings during the Mg97Zn1Y2 alloy extrusion process (see Figure 10) [41].The corresponding strain was observed to be huge for reduced ARLPSO.
It was also observed that the tensile strength declined as the temperature rose, as did ARLPSO.The result of the experimental work conducted using copper samples reveals that a larger scale's aspect ratio is substantially greater than a micro-scale's; furthermore, the aspect ratio rises with an increment in operating temperatures, maintaining a steady grain size with no lubrication.That is revealed in Figure 11 [42].

Experimental and simulation properties of extruded product
Research findings on the roughness of the surface, load of extrusion, microstructure, behavior of flow, strength, fracture, texture, hardness, wear, and so on of the extruded piece dependent on computational and experimental simulation of the casting and Ultra Fine Grain (UFG) content are presented as follows;

Microstructure
The surface morphology of extruded raw copper is not uniform in the case of coarse grain (CG) and homogeneous for the fine grain [43].With the decreasing size of the sample, ultra-fine grains (UFG) of aluminum alloy samples exhibit non-uniform flow.The inhomogeneous morphology of the Aluminum 6061 alloy grain distribution is presented in Figures 12 a and b, when the grains are extended at the edges (Figure 12b) relative to the central region where the force load is operating, and this is not responsible for the grain becoming lengthened due to high frictional factors.The investigation into an ECAP of extruded raw copper metal reveals an equiaxed structure (equal size of grain distribution in all directions) that surfaces after eight passes [44].The original size of the grain, 23.9 μm in the AZ31 sample via microgear extrusion, was reduced to 4.1 μm at the end of the six passes at 553 [45].The mean grain diameter (  ) is employed to calculate the microstructural size, which is computed using the longitudinal plane region (S) and the grain yield (  ) as described in Equation 5 [46].Researchers applied 150 and 20 μm sizes of copper sample grain collected by ECAP for more usage during extrusion.They noticed that grain limits were not obvious in the case of fine grains (20 m); This was caused by an upsurge in the material flow line with grain size reduction, as revealed in Figure 13.Grain size noticed was due to microstructural changes with the passes number and it is restricted to a specific passes number for the stipulated specimen, operating state, and the die configuration.

Extrusion load
The force required by the ram for aluminum alloy extrusion rises with a reduction in the size of the grain, as seen in numerical and experimental findings revealed in Figure 14 [48].Throughout the deformation of the Al 6063 sample, the force of the ram reduces with a rise in the sample size of the grain; this is attributed to a change in frictional influence between the billet and the container's wall [49].As demonstrated in Figure 15, the extrusion load needed for UFG of Al produced using the ECAP method exceed that required for CG material [50].Extrusion load rises owing to increased grain counts during micro-extrusion of aluminum.This was attributed to increasing friction as the grain's numbers increased.The greater the sample toughness, the greater the stress on the extrusion.When the aluminum alloy is extruded, the loads increase by increasing the height to the diameter ratio [51].For pure aluminum extrusion, the load of punch rises as the material is restricted back and sideways, which raises the velocity of the inner material quicker than that of the outer content, leading to a longer extruded billet.In the dead area of the punch-die cavity entry, non -uniform mechanical characteristics are discovered during a punch-blanking method for the production of aluminum micro-pins.[52].Due to this, load of extrusion increases indefinitely with smaller particle size, increasing coefficient of friction and grain size during the process of micro extrusion.

Flow stresses
The flow stress is measured by the amount of external surface grains and the interior sample grain volume.SPD applies extremely heavy pressure to each pass, minimizing displacement between grains and leading to smaller grain number [54].
Displacement relies on the grains of the inner volume instead of the outer surface grains as described in Equation 6 [55].In the event of a reduction in the specimen size at static grain size, the grains found within the sample become very limited relative to the exterior layer grains, leading to an increase in the total grain share (Nt): Hence, there is a reduction in flow stress.Through miniaturization of size, the proportion of surface grain (Ns) rises, resulting in lesser resistance to deformation and less hardening than grains within (Ni).The internal and external surface grain flow stresses are represented by   and   respectively: Flow stress boosts by lowering size of grains or adding to the grains number on a regular area of the surface [56].Barbier et al. (2009), employed various models of flow stress focused on the impact of structures of grains () and the impact of scale size () as observed in Equations 7 and 8. Their finding indicates that the material flow stress associated with the size of grain impact is more advantageous than effect of scale size, where   represents the original yield stress and p denotes the element of strain hardening.Flow stress associated with grains surface relies on the total length (wo), width cross-section (to) and mean size of the grain (L) as presented in Equation 7. Likewise, the size effect of the Equation 8 is attributed to the proportion of the original height (Ho) to the size of the grain.They discovered in their approach that flow stress becomes smaller as the percentage of original height to grain average size increases, which is true for micro-extrusion [58].Low temperature and high friction at the device work-piece interface also contribute to irregular flow with higher flow pressure, as demonstrated in pure copper extrusion.In the extrusion process, the surface grain upon shearing raises the hardness of the material, leading to increased flow stress.Couto et al. (2015), report that the flow stress in the micro-extrusion of raw copper is greater in material made of UFG relative to the material that is made of CG which can be seen in Figure 16.They discovered that high friction, low operating temperature, or work hardening could increase flow stress, and that the flow stress of UFG material is significantly higher than that of CG material [59].

Surface roughness
The surface irregularities or roughness is determined by the size of the grain as well as the height, which alters the coefficient of friction.Big grain size displays irregular spread with a rough surface quality in the deep drawing [60].Based on Bai and Yang (2013) findings, during the extrusion of the bronze phosphor C5191, the original surface roughness of 97 nm was reduced to 50 nm due to decreased vibration responsiveness.At the micro-extrusion (1 mm), they discovered that the coefficient of friction decreases with a fine surface die relative to a rough surface die, which is not relevant at the meso-scale [61].

Flow behavior of the sample
The flow action of the extruded sample varies with fluctuations in grain size and sample size.Figure 17 shows that the extruded pin curvature acquired from coarse grain (CG) material is greater than that of ultra fine grain (UFG) material [62].Curvature is determined by the size of the grains and their degree of freedom (DOF) [63].The DOF of the remaining grains is limited by the high grain number in UFG  Chan and Fu (2013), conducted a raw copper extrusion and discovered that the inner material flow in UFG is more than in CG material, resulting in an increase in the material's extruded length.Likewise, the lateral flow was observed to be higher in CG relative to UFG material.Backward extrusion material flow in UFG material is higher than in forwards extrusion [64].

Hardness
The hardness of the UFG aluminum alloy material prior to extrusion is greater than that of the CG material, but it altered after micro-extrusion for the specific sample size, as shown in Figures 18a and b 9, Figure 19 displays the flow stress of a Cu-Zn alloy material with increasing hardness (H).[66].The dislocation relies on the internal volume of the grain instead of outer layer of the grain and the stress of flow is corresponding to the hardness of the material; thus, the central zone of the extruded sample is tougher than the surface zone [67].

Tensile, yield and ultimate strengths
Chen and Tsai (2006) discovered that the material strength relies on the T / D (T= grain thickness, D= mean diameter of the grain) fraction represented as N.As illustrated in Figure 20, they discovered that the yield strength decreases as N decreases and then began to rise with a reduction in N.With decreasing grain size, the yield strength of a 2-mm billet at high strain rate (0.01) and temperature (520 K) reduced [68].

Fracture
Fracture is a material failure when the steady load applied gets fracture stress.Failures occur owing to slipping, cracking, or grains dislocation [70].The combination of stress and fracture strain has an inverse relationship to N 1/2 i.e., the T / D ratio (T= grain thickness, D= mean diameter of grain) as shown in Equations 10 and 11 and Figures 21a and 21b [69], Where I, h, k and l are considered as the numerical analyses of fracture stress-strain severity for various materials and improvements in fracture stress-strain with proportional N [69], found a linear drop-in   and   of pure copper with a reduction in grain diameter.
They express a fracture toughness (  ) of the polycrystalline material model as indicated in Equation 12, where    and    denote the grain interior and fracture toughness of the grain border zone, respectively,   and   are the inner grain and the volume proportions of the grain boundary zone, respectively.Findings show that size of grain reliance on yield strength is contrary to the Hall-Pitch correlation, and thus yield strength frequently decreases as grain size is reduced.Lowering the size of scale from macro to micro increases the possibility of the creation and microvoids collision during plastic deformation, which is the cause of material break up [69].Reducing the size of specimens or increasing the size of grain results in a decline in fracture toughness [71].Rosochowska et al. (2010), stated that the localization and fracture of the shear occurred from the fabrication of a micro-pin with a diameter of 0.15 mm using A1070 UFG alloy.As shown in Figure 22, Material fracture stress increases with a positive gradient (inner grain> grain boundary zone) and drops with a negative gradient (grain interior > grain boundary zone), although fracture tension is independent of grain boundary zone in zero gradients.[70].

Texture
Textures are sophisticated visible structures that are distinguished by their gradient, brightness, size, color, and so on [72].These visual structural properties are implied to include details about the lightness, consistency, direction, roughness, fineness, smoothness, etc. of the whole texture [73].The grain in isotropic materials are equal, but as the sample size decreases, there is variations [8].
Despite the identical symmetry of the UFG and CG material for the extruded specimen, the UFG texture is better than the CG.Super strength products made by ECAP methods retain the preceding texture upon extrusion [74].

Wear
Ultra-fine material wear resistance increases due to an increment in the amount of hardness, surface grains, and strength of materials [75].Extrusion techniques increase the wear strength of as-cast 6061Al alloy (Manjunatha and Dinesh, 2013).According to Soltani et al. (2014), hot extrusion enables enhanced wear resistance.The rate of wear in SPD processing is not homogenous for all materials but improves in grain refining [77].

Conclusion
Factors such as load, temperature, die angle, extrusion passes and friction are the factors that influenced the extrusion responses such as hardness, strength, surface smoothness, surface texture etc.The temperature as an input parameter can as well influence another input factors (low) by reducing the load required for extrusion process depends on the temperature setting.However, only few mathematical models on the extrusion have been reported.Therefore, there is need for development of different mathematical models from different researchers so as to further investigate the effect of the interaction of process parameters on the responses and to enables different extrusion company easy prediction of mechanical properties before the process /doi.org/10.1051/e3sconf/202343001216216 430

Figure 3 :
Figure 3: Limitation diagram of exit speed and temperature of the billet[20]

Figure 5 :
Figure 5: The influence of ram speed and material's temperature on the grain refinement of a 25 mm AA6060 bar (Nick and Chris, 2012).

Figure 8 :
Figure 8: Evolution of the temperature vs friction coefficient for NEPO ,DRY, VO and EPO during extrusion [34].

Figure 9 :
Figure 9: Experimental and predicted load variance with the original billet temperature for 2024 aluminum alloy[38].

Figure 10 :Figure 11 :
Figure 10: Average metal flow rate vs tensile yield strength at room and various temperature of extruded alloy Mg97Zn1Y2.[41]

Figure 17 :
Figure 17: Pattern of flow for sample of UFG and CG [65] [65].According toBai and Yang (2013), the Al 6061alloy increases from 1.5 to 3 GPa with less vibration during forging.They discovered that hardness increases until 20 vibration cycles and then stabilizes.Using Equation