Influence Of Extrusion On Microstructure And Mechanical Properties Of ZK60 Alloy

This paper took the ZK60 magnesium alloy as the research object. We did uniform heat treatment, extrusion experiment and aging treatment on this alloy after improving the original extrusion mold. Then the microstructure and Mechanical Properties of the sample at various states were tested. The main results were summarized as follows:1. The grain-boundary segregation was dissolved when the ZK60 as-cast alloy through uniform heat treatment and the intergranular was refined obviously. The intensity and the hardness of the ZK60 alloy were reduced and its extensibility was heightened greatly. The forming property got great improvement ultimately.2. We had done proper modification on the original mould by analyzing its application condition and combing the design theory on mould. Therefore, the extrusion experiment was completed. Then we carried the system analysis on the factors which affect the actual extrusion force, in order to provide the feasible reference for the design of extrude mold.3. The extrusion can improve the ZK60 magnesium alloy's organization effectively, and causes the substrate organization refined, at the same time the precipitated phase dispersive. When the extrusion ratio is 15, the crystal grain first refined and then grown up along with the extrusion temperature elevation, the precipitated phase increased at the same time; When the extrusion radio is not lower than 30, the crystal grew and the separation increased along with the extrusion temperature elevation. Its mechanical properties were related closely with the crystal grain size and the size of the precipitated phase. Under each extrusion radio, 300℃was the most ideal extrusion temperature. The alloy's organization was quite tiny evenly, and its overall mechanical properties were fine. At this extrusion temperature, its mechanical properties increased firstly and then reduced along with extrusion ratio elevation; and the rather larger extrusion radio was propitious to the crystal grain refinement and the separation of the precipitated phase. When the extrusion ratio is 30, its tensile strength, yield strength and the hardness were highest, the grain size was 5μm, the precipitated phase was approximately thick. When the extrusion radio is 45, the alloy's plasticity was best, and the grain size was approximately 3μm, the precipitated phase distributed dispersive.4. The extrusion parameter is mainly through controlling the crystal grain size and the separation content to influence the mechanical properties of ZK60 magnesium alloy. The mechanical properties of the alloy got the varying degree enhancement after extruding +aging. Especially, when the temperature is 300℃, and the extrusion ratio are 30 and 45 and though ageing, the alloy could get the superior comprehensive mechanical properties. Namelyσb=349.8MPa,σ0.2=318.2MPa,δ=22.8%, HB=80.6 for the former;σb =342.7MPa,σ0.2 =303MPa,δ=25.8%, HB=78.5 for the latter.5. There was thin precipitated phase in the organization of the extruded ZK60 alloy, when the extrusion temperature is 380℃. After aging (170℃×10h ), its grain didn't grow up, but the separation increased obviously and grown up partly. Thus caused the intensity and the solidity increased respectively, but the extensibility reduced.In a word, the paper had studied the influence rule of extrusion parameters on the microstructure and mechanical properties of ZK60 magnesium alloy mainly in the extrusion process, which supply the basis for the improvement of hot-working process and the improvement of product property.