气体保护熔炼条件下Mg-Gd-Y-Zr合金的夹杂物

本文研究了气体保护条件下,常规熔铸的Mg-Gd-Y-Zr合金中夹杂物的形貌、分布及形成原因,并通过计算分析了夹杂物的沉降行为.结果表明,Mg-Gd-Y-Zr合金中有MgO或Y的氧化物为主的球状、簇状、不规则状、线状的复合夹杂物和含熔剂夹杂物,夹杂物的平均尺寸为12.7μm,平均体积分数为0.26%.夹杂物出现的频率随其尺寸增大而急剧减小,尺寸在20μm以下的夹杂物占夹杂物总体积接近85%,尺寸在45μm以下的夹杂物占96%.计算结果表明,夹杂物沉降速率与其尺寸和密度相关;夹杂物密度增大,可使镁合金中夹杂物的最大尺寸减小,计算得到的合金中最大夹杂物的尺寸与实验结果基本一致.

INCLUSIONS IN Mg-Gd-Y-Zr ALLOY MELTING UNDER THE GAS COVERAGE

When smelting magnesium alloy under the protected conditions,it is unavoidable completely for magnesium alloy melt to react with the atmosphere,that the loose reaction products are separated very difficultly from the alloy melt.Finally,they become the inclusions in the alloy, to deteriorate the mechanical properties and performance.In this paper,in order to evaluate the inclusions in the new-style Mg-Gd-Y-Zr alloy and find an effective method of eliminating inclusions, the morphology,size distribution,species of inclusions and their formation in the alloy smelting and casting conventionally under gas coverage are analyzed.The settling behavior of the inclusions is also analyzed by the calculations.There are complex inclusion mainly composed of Mg or Y oxide and flux inclusion with spherical,cluster,irregular and linear shape in the Mg-Gd-Y-Zr alloy.The average size and volume fraction of them are 12.7μm and 0.26%,respectively.The frequency of the inclusions dramatically decreases with their size increasing.The volume of inclusions less than 20μm occupies nearly 85%of the total volume of inclusions,while the percentage of inclusions less than 45μm is 96%.The calculations show that the settling velocity of inclusions is dependent on their size and density,and increasing the inclusion density can diminish the maximal size of the inclusions in the magnesium alloy,which the maximal size by the calculations is consistent with the experimental result.