Achieving an ultra-high strength of high-Al-containing Mg-Al alloys via elements addition, extrusion and ageing treatment

Abstract The microstructure and mechanical property of peak-aged extruded Mg-11Al alloys with Ag and Sc addition were investigated by XRD, SEM, TEM and universal tensile machine. The microstructure of extruded Mg-11Al and Mg-11Al-1Ag alloys is composed of ɑ-Mg matrix and Mg 17 Al 12 phase. The rod-shaped and block-shaped Mg 17 Al 12 precipitates were observed in peak-aged extruded (PAE) Mg-11Al and Mg-11Al-1Ag-0.4Sc alloys. The orientation relationship between Mg 17 Al 12 precipitates and α -Mg matrix can be determined as: (110) β //(0002) α in PAE Mg-11Al-1Ag-0.4Sc alloy. And Ag, Sc addition increases the number density of Mg 17 Al 12 precipitates. The microstructure of PAE Mg-11Al-1Ag-0.4Sc alloy is composed of Mg 17 Al 12 precipitates, stable Al 3 Sc phase and α -Mg matrix with an average grain size about 1.51 μm. The PAE Mg-11Al-1Ag-0.4Sc alloy obtains an ultimate tensile strength (UTS) of 411 MPa and an elongation (EL) of 11.6%. The micro hardness value of PAE Mg-11Al-1Ag-0.4Sc alloy reaches 111 HV, which is obviously higher than that (103 HV) of PAE Mg-11Al alloy. The high-Al-containing Mg-Al alloy achieves a noticeable comprehensive mechanical property depending on elements addition, extrusion and ageing treatment. Corresponding mechanism was deeply discussed from grain refinement, solid solution strengthening, precipitation strengthening and second phase strengthening in this study.