Alloy Phases Control And Chemical Components Optimization Of ZK60 Magnesium Alloy

In this paper, the mechanism of how alloy phases formed and transferred in ZK60 magnesium alloy was determined. The influences of chemical components, casting technologies and heat-treatment technologies on parameters of alloy phases were analyzed. The results served as main principles to control alloy phases and optimize components.Morphology, category, amount and distribution of alloy phases were studied by using methodologies of metallurgical phase analysis, scanning electron microscopy (SEM) analysis, x-ray analysis, energy diffraction x-ray (EDX) analysis and transmission electron microscopy (TEM) in as-cast, solution-treated and as-aged ZK60 magnesium alloy. In addition, the effect of zinc, zirconium and yttrium on alloy phases was investigated on basis of ZK60 magnesium alloy.The research indicated that there was a great deal of eutectic with main components of a -Mg and MgZn. The eutectic had various morphologies and distributed in many ways. The two-stage solution technology (380C X 12h+510C X 12h) could effectively reduce the second phases and soften the matrix. MgZn2 phase, in form of parallelogram, 200nm to 500nm in length, having no fixed orientation relationship with matrix, not sensitive to heat treatment, was found in as-cast, solution-treated and as-aged ZK60 alloy as well. MgZn phase, in length of 500nm, had fixed orientation relationship with matrix. Mg2Zn3 phase, in form of 100nm short rob, was the most fine phase in terms of size and the most even phase in terms of distribution in ZK60 alloy.With the increase of zinc content, the amount of eutectic went down first and then went up, the dimension and distribution of which, however, got more and more fine and even. With the increase of zirconium content, the amount of binary Mg-Zn phases decreased intensively. Zirconium could not only fine the grain but also form precipitation phase and even present as zirconium particles. Alloy containing yttrium had fish-bone-like eutectic structure and continuous reticulation structure at triangle boundary or around the grain. Quantitative analysis of fish-bone-like structure showed that it consisted of Mg-Zn binaryphase and Mg-Zn-Y ternary phase and the continuous reticulation structure was also Mg-Zn-Y ternary, which divorced from fish-bone-like structure.