Micro-mechanisms of rate dependent tensile deformation for LY12 aluminium alloy

The great change of LY12 alloy property took place after the alloy underwent high temperature and low strain rates (elongation up to 17%) followed by room-temperature tension. It was found that the flow stress of LY12 aluminum alloy reduced to only ten percent of the yield point after undergoing high-temperature deformation at low strain rate (10^-4 s^-1), and the elongation to fracture increased by one time. This abnormal room-temperature property strongly depends on the tensile strain rates and temperature and the cooling rate. By comparison, the sample subjected to high-temperature deformation at higher strain rate (10^-1 s^-1) showed brittle-like behavior after cooled up to room temperature, i.e. a sudden increase in flow stress and rupture quickly. From the point view of precipitate and substructures, the characteristics of microstructure are described by TEM analyses. Combined with SEM fracture surface analysis, the corresponding fracture mode and mechanisms are expatiated.