Effects Of Alloying And External Fields On The Mg-Li-Al Alloys

With energy crisis and attention of environment protection,light-weight and recyclable materials are in great need.As the lightest alloys among the known metals and alloys,Mg-Li alloys have been attractively investigated and have the application potential in the fields of aerospace,aircraft structures,automobile and electric industry as well as for structural components in ultra-light communication systems.In this paper,the effects of electromagnetic stirring,Ca and combined electromagnetic stirring and Ca on the microstructures and mechanical properties of Mg-8%Li-3%Al alloys were studied,and the relationship between the chemical composition,microstructures and mechanical properties were discussed.Microstructures of alloys were observed and studied by means of optical microscope(OM),scanning electron microscope(SEM),and X-Ray diffraction and so on.The Brinell hardness and tensile properties were measured.Effects of electromagnetic stirring on the heat treatment behavior of Mg-8%Li-3%Al alloys were studied.Experimental results show that the electromagnetic stirring,Ca and combined electromagnetic stirring and Ca all improve the microstructures and mechanical properties of Mg-8%Li-3%Al alloys.When the electromagnetic stirring voltage is 100V,the microstructure is refined and the tensile strength,elongation and Brinell hardness reach to 212.9MPa,10.5% and 71.3HB.With 0.5%Ca addition to the as-cast alloys,theβphase gets thinner,and the tensile strength and elongation reach to 188.93MPa and 11.35%.When the electromagnetic stirring voltage is 80V,0.5%Ca addition could make the microstructure fine and uniform, and the tensile strength and Brinell hardness is67.5HB and 203.8MPa with the elongation of 7.7%.The experimental results of heat treatments show that with the increase of the quenching temperature(150℃～350℃),the solution of Mg and Al in solidβphase increases,and the Brinell hardness of the alloy increases as well.Aging peak and over aging happen becauseθ(MgLi₂Al) which precipitates in theβmatrix and strengthens the alloy is unstable and transforms to stable AlLi phase.Aging curves of EMS specimens change in a smaller amplitude. Besides,the effects of ultrasonic field on the structure and properties of the AZ31 alloys were simply studied in this paper.The results show that ultrasonic field could refine the grain and the second phase,and improve the tensile properties of the AZ31 alloys.