A356合金低温拉伸力学性能变化机理研究OACSTPCD

The tensile mechanical properties of A356 alloy were tested at 20 ℃,-20 ℃,-40 ℃,-60 ℃ and-80 ℃.The fracture morphologies and the microstructures at 20 ℃,-20 ℃ and-60 ℃ were researched by SEM and optical microscopy.The deep etching morphologies of damaged Si particles and dislocation slip band in the tensile specimens were investigated.The results showed that the tensile strength and yield strength increased,and the ductility decreased when the temperature dropped from 20 ℃ to-80 ℃.The dislocations piled up in ahead of Si phases during tensile test,which caused Si phase to crack.The stresses concentration in these cracks tip,which made the alloy to fracture before the large plastic deformation occurred.This is the main reason affecting the low temperature plasticity of the A356 alloy.With the temperature dropped,the Peirls-Nabarrro force of aluminum increased,which caused the dislocations motions difficultly in the process of plastic deformation.So the tensile strength,yield strength and hardening exponent increased at low temperature,which caused the plastic deformation of the whole sample tended to homogenization.