The Effect Of Additional Elements Cr And Sr Aging Process Of ZA102 Magnesium Alloy

In this paper,the effect of element Cr or Sr on microstructure of ZA102 magnesium alloy was studied by SEM and HRTEM, the structure of the phase of test alloy was studied by XRD, The effect of the precipitation kinetics was studied by DSC.The results showed that: the addition of Cr results in refinement of grain in as-cast alloy, network organization ofβ-Mg₁₇Al₁₂ was interrupted with dispersively distributed, new phase of CrSb2 was formed. The hardness of the alloy get improved by adding amount of Cr, the maximum value was up to 99.7HV0.2, the hardness increases the amount of 21%. Cr could improve the rate of hardness, The hardness get increased of 131.8 HV0.2 of the alloy is up to 95% of maximum hardness level ,after aging 8h, the maximum hardness is higher the amount of 23% compared with non-adding Cr of test alloy,Hardness declines slowly in the over-aged.Cr could accelerate atomic segregation, the precipitates of test alloy show vermiculate distribution at early aging,the test alloy have stability of precipitates, which inhibits the growth of precipitates aging latter part.precipitates are tiny and dispersive in the peak aging, some precipitates parallel with {0001}Mg, others intersect with{0001}Mg, this interactions of precipitation phase and dislocation contribute to strength. DSC analysis shows that the activation energy of the alloy adding Cr was down to 6.637K/mol, the age-hardening rate was improved.The addition of Sr results in grain refinement of alloy Significantly, Reticulation ofβwas interrupted ,Granularly distributed.Mg32(Al,Zn)49 and a small amount of phases of Mg17Sr2,Al4Sr were observed in the alloy, The hardness of the alloy by adding content of Sr, the maximum value is up to 87.8HV0.2.But Precipitates of test alloy added Sr grow up fastly,precipitate which are (short) rod-shaped and needle-like(Al4Sr) can split the alloy matrix and makes hardness dropped significantly, Therefore, heat treatment of this alloy is not much significance.In general, although the addition of Sr results in grain refinement of alloy Significantly,the precipitates grow up fastly in the aging process,test alloys are not well reinforced.Not only dose adding Cr improve the cast structure of alloy,but also promote aging hardening, the organization of the test alloys are tiny and dispersive, Therefore, adding Cr element is effective.