Microstructures And Properties Of Reciprocating Extruded ZK60 Alloy

The commercial ZK60 magnesium alloy has the highest strength. Increasing its plasticity is very significant for enlarged its application. In this paper, the microstructures were improved by reciprocating extrusion (RE) and heat treatment, while the properties were optimized. Firstly, ZK60 magnesium alloy was prepared by reciprocating extrusion on different processes, microstructures and properties before and after extrusion were studied. Then RE-n-EX-ZK60-CT magnesium alloys were heat-treated, the effects of heat treatment on the microstructures and properties were analyzed. OM, SEM, TEM, XRD, DTA, tensile tests, hardness tests and TMA were used to observe microstructures and evaluate properties,respectively. The main results are as follows:(1) Reciprocating extrusion can refine the microstructures of ZK60 magnesium alloys effectively, and decrease melting point in some degree, and microstructures were uniformity, and reinforcement phases are dispersed. With the increase of extrusion temperatures, grains were fined, and then grown up, precipitated phases fraction was increased. 335℃was the ideal extrusion temperature, the microstructures were fine and uniform, mechanical properties were the best processed at this temperature. With the increase of extrusion passes, grains were refinement and reinforcement phases were precipitated. For RE-4-EX-ZK60-CT magnesium alloy, grains were about 6μm equiaxed grain, precipitates were fine, uniform. The most feature of RE-n-EX-ZK60-CT magnesium alloys is its high plasticity, the elongation of RE-2-EX-ZK60-CT magnesium alloy is the highest, about 17.93%.(2) The reasonable heat treatment processes were 120℃×12h artificial aging (T5) and 330℃×12h complete annealing (O). After 120℃×12h artificial aging, the hardness of RE-n-EX-ZK60-CT(n are 2, 4 and 8, respectively)magnesium alloys were 90.76HV5, 82.58HV5 and 84.2HV5, respectively. Heat treatment can dramatic increase the elongations of the REZK60 magnesium alloy, the elongation of RE-2-EX-ZK60-CT magnesium alloy was 24.87% after T5 and O heat treatments.(3) After reciprocation extruded by small mould, the refinements of microstructures were obvious. Grain sizes were 1.5μm~5μm. After 120℃×15h artificial aging, the elongation of alloys was 40%, the strengths were equivalence to that after RE and T5 from big mould. The refine mechanic of RE-n-EX-ZK60-CT magnesium alloys was DRX refining and particle refining; the formed mechanic of DRX was main of continuous DRX; the mostly deformed mechanic was dislocation moving, grain boundary sliding and diffusion creeping.