Investigation On Microstructure And Properties Of High Strength Die Casting Mg-Zn-Al Alloys

As the development of auto industry and the improvement of social environmental awareness,lightweight of automobile becomes more and more important.In the future,auto parts that are made of magnesium alloys will increase.Since the strength of normal Mg-Al series die casting alloys is low,it is pressed for high strength magnesium die casting alloys.The goal of the project is to develop a high strength Mg-Zn series die casting alloys.The alloy is required excellent castibility and after T6treated,the yield strength of the alloy shoule be exceed 200MPa.In the paper,hot tearing susceptibility?HTS?,microstructure and mechanical properties of die casting Mg-xZn?x=8%,10%,12%?and Mg-10Zn-yAl?y=0,2%,3.5%,5%?alloys?ZA series alloys?have been investigated.The HTS of alloys was investigated using rod die casting mold and was determined based on the location and quantity of cracks in rods.The HTS results show that Al is effective to improve the hot tearing resistance of ZA series alloys.The HTS value of ZA105 alloy is the lowest.Thermodynamic calculation software?Pandat8.0?was used to calculate solidification paths of ZA series alloys and found that the correlation between HTS and F_lep?liquid fraction at the end of primary solidification?is negative.The correlation between HTS and FTR?freezing temperature range?is positive.The EDS and XRD analysis of as-cast ZA series alloys show that Mg₅Zn₂ phase exists in Mg-10Zn alloy and quasicrystal phase(Mg_62-69Zn_22-25Al_6-16)exists in other alloys.After T4 treatment,Mg₅Zn₂phase transforms into MgZn???phase,quasicrystal phase transforms into MgZn*phase in ZA102 alloy and Al₅Mg₁₁Zn₄*phase in ZA103.5 and ZA105 alloys.The mechanical properties of ZA105 alloy in T6 condition are 209MPa,311MPa,3.3%respectively,which showing significant precipitation hardening response.The peak hardness of ZA series alloys is improved and the aging kinetics is also accelerated with increasing the content of Al.The result shows that the elongation of ZA105 alloy is improved 40%by vacuum die casting.The second phases in ZA105 alloy is modified by Ce?0.5wt.%?and the elongation is improved 20%.