Deformation and densification behavior of discrete media filled thin-walled tubes during forward extrusion

Discrete media filled thin-walled hollow profiles are frequently used as integer structures for special purpose, e.g., in certain materials processing or architectural components. To understand the deformation of such composite structures which is a complicate mechanics process, involving coupled elastic-plastic deformation of dense metal, compaction of particle and interaction between the filler and the wall, the forward extrusion of Al 6061 tubes filled with various particles was studied. The analysis regarding internal volume variation of round tubes during forward extrusion indicates that with the diameter reduction the volume of tubes decreases commonly. The cavity shrinkage brings about triaxial pressure on the filler, resulted in compaction and densification of it. Loose powders filling leads to higher extrusion load. Due to dissimilar migration behaviors of the particles, the load?stroke curves of the tubes filled with fine powders and coarse balls are quite different. Small Lankford value of the tube wall material leads to higher hydrostatic pressure of the filler and then more powders are compacted.

Dynamic recrystallization behavior of AZ31 magnesium alloy processed by alternate forward extrusion

One of the important factors that affect the microstructure and properties of extruded products is recrystallization behavior. Alternate forward extrusion （AFE） is a new type of metal extrusion process with strong potential. In this paper, we carried out the AFE process experiments of as-cast AZ31 magnesium alloy and obtained extrusion bar whose microstructure and deformation mechanism were analyzed by means of optical microscopy, electron backscattered diffraction and transmission electron microscopy. The experimental results indicated that homogeneous fine-grained structure with mean grain size of 3.91 pm was obtained after AFE at 573 K. The dominant reason of grain refinement was considered the dynamic recrystallization （DRX） induced by strain localization and shear plastic deformation. In the 573-673 K range, the yield strength, tensile strength and elongation of the composite mechanical properties are reduced accordingly with the increase of the forming temperature. Shown as in relevant statistics, the proportion of the large-angle grain boundaries decreased significantly. The above results provide an important scientific basis of the scheme formulation and active control on microstructure and property for AZ31 magnesium alloy AFE process.

Microstructure Evolution and Deformation Behavior of AZ31 Magnesium Alloy During Alternate Forward Extrusion

The paper presents a new extrusion method, alternate forward extrusion, in which the punch was replaced with double-split structures so as to achieve the grain refinement for material near the interface of double-split structures. The results showed that the unique loading mode made metal flow sequence and behavior significantly changed during alternate forward extrusion. The additional shear deformation produced by the double-split punch structures resulted in a refining effect on the microstructure of the blank, which was then further refined during flow through the die orifice owing to shear deformation. Compared with the conventional extrusion, the recrystallization process in the alternate forward extrusion process produced grains that were smaller and more homogeneous in size. The recrystallization process was more abundant, and the dislocation density was significantly increased. It can be concluded that the alternate forward extrusion process could achieve fine-grained strengthening, which provided technical support and scientific guidance for the engi- neering application of magnesium alloy extrusion forming technology.

Test of Friction Parameters in Bulk Metal Forming Based on Forward Extrusion Processes

Existing methods for examining the friction parameters in metal forming all have advantages and disadvantages.Based on the theory of plasticity,the current study established quantitative correlations among friction coefficient/factor,yield stress of the workpiece material,load and die geometry in the forward extrusion with a conical die,and then designed a procedure for testing the friction parameters in forming processes using the correlations.A series of extrusion experiments along with the numerical simulations,using AA 7050 specimens under various lubricating conditions,were carried out.The results proved that the method can obtain the friction coefficient/factor with an acceptable precision.Theoretically,since the effects of material properties,forming velocity,temperature and surficial condition,etc.,on the deformation can be directly considered in the operation,this method is applicable to a wide range of material types and forming conditions.To avoid the occurrence of "barreling phenomenon" under large load which may lead to failure of the operation,it is recommended that half angle of the conical die ranges from 5 to 10 degrees.

Forward hot extrusion forming process of 4-lobe aluminum alloy helical surface rotor

The 4-lobe aluminum alloy helical surface rotors are widely applied in industry,such as superchargers.Generally,the conventional manufacturing processes of aluminum alloy helical surface are time consuming and costly.To make the manufacturing processes more flexible and economical,the forward hot extrusion process is proposed to form the 4-lobe aluminum alloy helical surface rotors.In this work,we implement both simulations and experiments to the forming process of the helical surface,of which the material is 6063 aluminum alloy.The forward hot extrusion process is simulated with finite element method in DEFORM-3D.Based on the simulation method,the influences of different extrusion parameters,such as extrusion temperature,extrusion speed and extrusion ratio,on the extrusion process are studied.According to the numerical simulation results,the optimal case is chosen to carry out the experiment.Furthermore,the experimental results show that the surface is smooth;the toothed fill is full;the twist angle in the length direction is evenly distributed;the value of twist angle is roughly in line with the design angle,which is mainly due to the modified die structure,having a positive and significant effect on the increment of twist angle.Therefore,the twist angle has an increase of about 76%,which verifies the modified die structure.

ANALYSIS OF SURFACE CRACK ON FORWARD EXTRUDING BAR DURING AXISYMMETRIC CUP-BAR COMBINED EXTRUSION PROCESS

In this paper, the kinematically admissible velocity field with surface crack on forward extruding bar is put forward during the axisymmetric cup-bar combined extrusion process, in accordance with the results of model experiments.On the basis of velocity field, the necessary condition for surface crack formation on the forward extruding bar is derived, with the help of upper bound theorem and the minimum energy principle. Meanwhile, the relationships between surface crack formation and combination of reduction in area for the part of forward and backward extursions relative residual thickness of billet (T/R0),frictional factor (m) or relative land length of ram and chamber are calculated during the extrusion process. Therefore, whether the surface crack on forward exturding bar occurs can be predicted before extruding the lower-plasticity metals for axisymmetric cup-bar combined extrusion process.The analytical results agree very well with experimental results of aluminium alloy LY12 (ASTM 2024) and LC4 (ASTM 7075).

Polycrystal modeling of hot extrusion texture of AZ80 magnesium alloy

The visco-plastic self-consistent (VPSC) model is extended to take the dynamical recrystallization (DRX) into account so that the hot extrusion texture of AZ80 magnesium alloy can be properly modeled. The effects of extrusion temperatures and imposed boundary conditions on the resulting textures were investigated, and good agreement can be found between the simulated and the measured extrusion textures. The simulated results show that the DRX grains are responsible for the formation of the {2110} fiber component since the {1010} poles of the DRX grains are tilted away from those of the unrecrystallized grains during the formation of their high angle boundaries (HABs). Furthermore, the basal poles of the grains are favorably oriented to the transversal direction (TD) where the imposed deformation is larger due to lower slip resistance of the basal slip. The elevated temperature enhances the activity of pyramidal ?c+a? slip modes and gives rise to a larger recrystallized volume fraction, resulting in a weakened extrusion texture.

Influence of homogenizing on mechanical properties of as-cast AZ31 magnesium alloy

Forward extrusion experiments of as-cast AZ31 magnesium alloy were conducted at different temperatures and different extrusion ratios using the as-cast billets with and without homogenizing treatment.The mechanical properties of pre-and post-extrusion of the two kinds of billets were investigated.Experimental results show that the mechanical properties of post-extrusion of the two kinds of billets all are obviously improved compared with those of pre-extrusion.The elongation of post-extrusion using the billet with homogenizing is higher than that without homogenizing,but the tensile strength is lower than that without homogenizing.When the extrusion ratio increases,the elongation and tensile strength of post-extrusion of two kinds of billets all will increase obviously.When the extrusion temperature of billet without homogenizing increases,the tensile strength of post-extrusion will decrease obviously and the elongation of post-extrusion will change to a small extent.For the billet with homogenizing,the tensile strength of post-extrusion will decrease in some sort when extrusion temperature increases.

NEW TECHNOLOGY AND MACHINE TOOL FOR THE FORMING OF THE REAR AXLE SHAFT OF LIGHT TRUCK

A new technology of forward extrusion and cross rolling has been developed to process the rear axle shaft sleeve of light truck with the use of tube billets. This technology is characterized by large reductions of material, energy and cost of production and has significant economical benefits. This technology is stable and reliable. The three rolls transverse rolling mill built based on this technology has novelty construction, higher production efficiency, non-vibration and noise. The research results have been extensively applied to light trucks and farm transport with load of 1 to 3 tones.