ANALYSIS OF COEXISTENCE OF TWO KINDS OF MACRO-DEFECTS IN CUP-CUP AXISYMMETRIC COMBINED EXTRUSION

In this paper, the relationships between the region of the two coexisting kinds of macro-defects and the reduction in area, as well as between the region and the relative residual thickness of the billet are studied for the cup-cup axisymmetric combined extrusion, on the basis of the analytical expression obtained by the upper-bound approach. The presented model and conclusions are confirmed by the experimental results in this paper.

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).

THE METHOD OF PHOTOPLASTIC SIMULATION AND ITS APPLICATION ON COMPLICATED DEFORMATION

The paper concisely introduced the hoopment of photoplastic simulation and the principle of its appli- cation.Deformations of combine extrusion and strain distributin in the process of upsetting the cylinder with void were studied by this physical photoplasic simulation method. Some important informations obtained from the simulation experiment are helpful to understand the deformation law and the charac- teristics of material flowing.The validity of the physical simulation method and the importance of com- bining the physical simulation method with numerical simulation method together were proposed in the paper.

Effect of Extrusion Combination Types on Microstructure and Mechanical Properties of the AZ31/GW103K Bimetallic Composite Plates

The AZ31/GW103 K bimetallic composite plates were prepared by co-extrusion of different combination types(sandwich extrusion type and double semicircle extrusion type),and effects of different extrusion combination types on the microstructure and mechanical properties of bimetallic composite plates were systematically investigated.The results show that both the AZ31/GW103 K bimetallic composite plates prepared by different extrusion combination types have good metallurgical bonding,and changing the combination type does not affect the thickness of the interfacial transition layer of composite plates.Compared with the monolithic AZ31 and GW103 K extruded plates,co-extrusion can promote the dynamic recrystallization(DRX)of AZ31 and GW103 K components in composite plates,and double semicircular extrusion type has a better promotion effect on the DRX than sandwich extrusion type.In addition,the texture of AZ31 in both monolithic AZ31 and AZ31/GW103 K/AZ31(A/G/A)plates is a typical(0002)basal texture,while that in the AZ31/GW103 K(A/G)composite plate shifts to the tangent direction(TD)of extruded plate.Compared with the monolithic AZ31 extruded plate,both the yield strength and tensile strength of A/G and A/G/A bimetallic composite plates are significantly improved.The strength of A/G/A composite plate is higher than that of A/G composite plate,but its elongation is worse.Meanwhile,co-extrusion reduces the dislocation density of AZ31 and GW 103 K components in composite plates,and different extrusion combination types also affect the dislocation density.