Study On The Microstructure, Mechanical Properties And Hot Deformation Behavior Of Mg-Al-Mn-Si Wrought Magnesium Alloy

Based on the research of Mg-3Al-0.4Mn magnesium alloy which developed by Yingxin Wang, several wrought magnesium alloys with different Si content were prepared by adding Si into AM30 alloy.In this paper, the effect of Si on the microstructure and mechanical properties of AM 30 alloy were studied by using optical microscopy (OM),X-ray diffractometer (XRD) and scanning electron microscopy (SEM). The flow stress-strain curves of AM30-0.1Si and AM30-0.5Si alloys were obtained by using isothermal hot compressive test; the extrusion limit diagrams of these two alloys were constructed. The hot deformation behavior and microstructures evolution of these two alloys during deformation process were also studied. The results show that:Si has the effect of grain refinement on AM30-xSi alloy, grain size decrease with the increasing of Si content. The grain size of AM30 alloys as-cast decrease from original 80μm to 67μm with 1% Si added, along with the grain size of AM30 alloys as-extruded decrease from original 21μm to 15μm with 1% Si added. The mechanics properties of AM30-xSi alloys as-cast decrease with the increasing of Si content. UTS decrease from 198Mpa to 177Mpa, along with the TYS decrease from 58Mpa to 48Mpa, and Elongation decrease from 14.3% to 8.6%. After extrusion, The mechanics properties of AM30-xSi alloys improve, and mechanics properties increase with the increasing of Si content. TYS and UTS of AM30-1Si alloy separately reaches 190Mpa and 285MPa, which is highest in AM30-xSi alloys. But Elongation only reaches 11.0%. The best T5 ageing technique is 200℃-4h which can almost improve the mechanical properties of AM 30-xSi alloys.The hyperbolic sine equation can be used to describe the relationship between flow stress and strain rate, deformation temperature of AM30-0.1Si and AM30-0.5Si alloys under all stress. The materials' constants are calculated as follows:(1)For AM30-0.1Si alloy, the strain hardening factor n is 5.597, average deformation activity energy Q is 180Kj/mol, the relationship between peak flow stress and Z can be expressed as ln[sinh(aσp)]=-5.34047+0.18365lnZ.(1)For AM30-0.3Si alloy, the strain hardening factor n is 5.462, average deformation activity energy Q is 186Kj/mol, the relationship between peak flow stress and Z can be expressed as ln[sinh(aσp)]=-5.4739+0.18769lnZ.According to the relationship between corrected peak stress and Z parameter, combining the calculating formula of extrusion force p =σ(0 .171+1.86lnR+4mlb /db3) and calculating formula of temperature riseΔT =σlnλ/ 3ρCp, the extrusion limit diagrams of AM30-0.1Si and AM30-0.5Si alloys are constructed. Comparison of the extrusion limit diagrams of AM30-0.1Si and AM30-0.5Si alloys, it is found that the extrudablility of AM30 alloy decrease when Si added, but Si content almost has no influence on the extrudablility of AM30-xSi alloy.Si can promote the process of the dynamic recrystallization in hot deformation when Si added to AM30 alloy. With the content of Si in AM30 alloy increase, the dynamic recrystallization is more easily in hot deformation at the lower deforming temperature(200-300℃) or fast strain rate(1S-1). At a certain strain rate in hot deformation, temperature rise will make it easy for dynamic recrystallization occurring and recrystallization grains growing, When the deformation temperature unchanged, the increase of strain rate is unfavorable to the dynamic recrystallization, With the increase of strain, there will be higher density dislocation in grain, which promotes occurring of dynamic recrystallization.