Enhancement of the Low Temperature Deformation Ability of Magnesium Alloys

Abstract

In general, magnesium alloys exhibit the attractive combinations of low densities (1.74 g/cm3 versus 2.7 g/cm3 for Al) and high specific strength values (comparable or greater than that of precipitation strengthened Al alloys), along with good damping capacity, castability, weldability, and machinability. Conventional magnesium alloys can be divided into five main groups (Mg-Al-Zn, Mg-Zn-Zr, MgRare Earth-Zr, Mg-Th-Al, Mg-Li-Al) and among these alloys, those developed from the Mg-Al-Zn ternary system (i.e. coded as AZ alloys) have found great interest and the vast number of industrial applications. The main objective of this thesis is to enhance the mechanical properties of AZ31 and AZ91 Mg alloys. AZ31 and AZ91 magnesium alloy plates with 3% and 9% aluminum respectively were purchased from Turkey and China. AZ31 and AZ91 samples were homogenized at 400°C for 2 hours and at 425°C for 15 minutes respectively to break up the casting microstructure and to eliminate chemical inhomogeneity. Both alloys were aged at 150-200-250°C for 1-5-10-24-50-100 hours to see the effect of aging on the microstructural evolution and its influence on the evolution of mechanical properties of these alloys. Furthermore, aging under stress experiments were performed at the same temperature for one hour, by applying constant stress values (20, 40, 60 and 80 MPa) which are in the elastic range of the alloys. The influence of these thermomechanical processes on the evolution of microstructures and mechanical properties was investigated and compared with the aged samples.