Hot tensile behavior and deformation mechanism of Mg–5Al–2Ca alloy influenced by SiC particles

Abstract

Multiple physical and metallurgical influences exerted by SiC particles (SiCp) still make it difficult to understand that how the addition of SiCp affects the hot tensile deformation behavior of Mg matrix alloy. A deformation mechanism analysis method developed in this study is promising to find a reasonable answer on this problem, via the comparison of SiCp/Mg–5Al–2Ca composite (SiCp/AC52) and Mg–5Al–2Ca alloy (AC52). The effects of SiCp on the constitutive description, deformation mechanism, strain hardening and softening behavior are specially investigated based on the microstructure evolutions, true stress-strain behaviors and fracture characteristics of the uniaxial tensile tests under the deformation temperatures of 290–350 °C and strain rates of 8.3 × 10−4-1.67 × 10−2 s−1. The grains exhibit different growth levels during the hot tensile deformation, and it becomes more evident with the decrease in the strain rate and the increase in the temperature. The addition of SiCp restrains grain growth and leads to a refined and homogeneous grain microstructure. The flow stress at low strain rate is increased with the addition of SiCp, while, which is decreased by SiCp when the strain rate over 8.3 × 10−3 s−1. The addition of SiCp leads to the tress exponent value n and the activation energy value Q increasing from 1.56 and 90.33 kJ/mol to 2.94 and 110.77 kJ/mol, respectively. The dominating deformation mechanism is altered corresponding to the strain rate. The addition of SiCp causes the local stress/strain redistribution, restrains the grain boundary sliding and facilitates the dislocation climb creep in the hot tensile deformation. Moreover, such addition stimulates the generation and coalescence of previously-induced small voids or dimples, while inhibits its extension and enlargement. As a result, the fracture morphologies exhibit an intergranular ductile fracture combined with micro-dimple growth and coalescence.