Effect Of Rare Earth On The Casting Properties Of Mg-4Al Alloy

Due to the increasingly serious problems caused by energy crisis, and the urgent need for a good living environment, as usual metal structure materials in the lightest metal, there is a sharp increase in the amount of magnesium alloy, and the expectations of good mechanical properties of magnesium alloy are also need growing. In actual production, Mg-4Al magnesium alloy is a widely used cast magnesium alloy, the β-Mg17Al12 phase in the microstructure and the Oxidation debris from molten metal in the process of pouring is a key factor affecting its casting fluidity, limiting its application of the auto parts product which needs good filling capability, and other precision.Taking the Mg-4Al-RE alloy adding mischmetal (Ce-La-Nd-Pr) as the research object, referencing to the unprocessed Mg-4Al alloy, using triple helix sand mold, the effect of rare earth on the casting properties of Mg-4Al alloy were investigated. By using ladder sand mold, the influence of cooling rate on the microstructure and properties of Mg-4Al alloy was studied. The corrosion inhibition effect of rare earth by polarization curve measurements. The research results show that rare earth in Mg-4Al can increase the fluidity by average 30%(at least by 16%, at most by 45.7%). The reaction of RE and Al,Mn in magnesium alloy melt is priority, forming the intermediate phase, rare earth reacts with aluminum element in magnesium alloy and form needle-shape compound Al11Ce3 and Al11La3 and form Al10(Ce,La)2Mn7 as grainy, which can refine the as-cast microstructures of Mg-4Al-RE alloy, and effectively inhibit the formation of the β-Mg17Al12 phase. The study results show that rare earth is priority to react with Al and Mn magnesium alloy melt, forming an intermediate compound, which can refine its cast organization and effectively inhibit the β-Mg17Al12 phase formation. In this study, the nucleation rate was promoted by Al11Ce3、Al11La3 and Al10(Ce,La)2Mn7 phase, generating precipitation strengthening and improving Mg-4Al hardness and corrosion resistance. With increasing cooling rate, the crystal grains can be refined, which can also improve Mg-4Al-RE hardness and corrosion resistance. To sum up, through the way of adding rare earth, the cast fluidity can be effectively increased, hardness and corrosion resistance can be improved. By increasing cooling rate, besides the grain size of Mg-4Al-RE alloy can be further refined,, hardness and corrosion resistance can also be improved.