Monotonic and Cyclic Plasticity Response of Magnesium Alloy. Part I. Experimental Response of a High‐Pressure Die Cast AM60B

Abstract: The mechanical behaviours of a high‐pressure die cast AM60B magnesium alloy were studied. Monotonic and cyclic tests (with a strain ratio R = ?1) were carried out at ambient temperature. The results of the mechanical testing were discussed with respect to the crystallographic texture and the microstructure of the alloy in terms of clusters of pores, grain size, second phase strengthening as well as the orientation‐dependent activation of different deformation mechanisms such as slip and twinning.     

铸态ZK60 镁合金往复挤压的组织与性能

目的探索工艺参数对微观组织和力学性能的影响。方法材料选用铸态ZK60合金,通过试验研究挤压比、往复挤压道次对镁合金微观组织演变的影响,分析挤压比对T6处理的材料力学性能的影响。结果在一定范围内增大挤压比和增加往复挤压道次均有助于组织细化。在350℃、挤压比为8时,经过8道次往复挤压变形可以细化晶粒到3μm左右。晶粒尺寸达到5μm以下,增加往复道次使晶粒细化的效果不明显,但有利于晶粒的均匀化。在往复挤压温度350℃,挤压比8,往复道次8的条件下,经过T6处理的试样具有良好的综合力学性能,伸长率达到22.1%,抗拉强度为308.6 MPa。结论 ZK60镁合金在往复挤压和动态再结晶过程中,晶粒的细化与往复挤压道次和挤压比有关。若挤压比较小,尽管往复道次较大,但是晶粒细化的效果不明显;合理的匹配挤压比与往复道次,能获得细小、均匀的组织。     

Implementation of cyclic plasticity models based on a general form of kinematic hardening

This paper deals with implementation of cyclic plastic constitutive models in which a general form of strain hardening and dynamic recovery is employed to represent the multilinear, as well as non‐linear, evolution of back stress. First, in order to incorporate such a general form of kinematic hardening in finite element methods, successive substitution and its convergence are discussed for implicitly integrating stress; moreover, a new expression of consistent tangent modulus is derived by introducing a set of fourth‐rank constitutive parameters into discretized kinematic hardening. Then, the constitutive parameters introduced are specified in three cases of the general form of kinematic hardening; the three cases have distinct capabilities of simulating ratcheting and cyclic stress relaxation. Numerical examples are given to verify the convergence in successive substitution and the new expression of consistent tangent stiffness. Error maps for implicitly integrating stress under non‐proportional as well as proportional loading are also given to show that the multilinear case of the general form provides high accuracy even if strain increment is very large. Copyright © 2002 John Wiley & Sons, Ltd.