ZK60 magnezyum alaşımının termo-mekanik işleme sonrası düşük sıcaklık davranışı

Due to its low weight and good combination of mechanical strength and formability, wrought magnesium alloys containing zinc and zirconium are widely used in automotive and aerospace industries. Since mechanical properties of pure magnesium are weak, the addition of alloying elements is used to improve the mechanical response of magnesium alloys. In this study, ZK60 wrought alloy was selected to improve its mechanical properties using thermo-mechanical processes. A systematic combination of heat treatment and warm rolling was applied for this purpose. The solution treated sample was exposed to rolling followed by annealing treatment for enhancing the formability. Static and under stress regimes of aging were performed to form fine precipitates in the Mg matrix. The low temperature tensile behavior of samples was investigated at temperatures of -60℃, -20℃ and ambient temperature at a quasi-static strain rate of 10-3 s-1. The effect of processing parameters including heat treatment, deformation and aging on the microstructure, texture and mechanical behavior of samples were characterized as well. It was shown that systematic thermo-mechanical processes can significantly refine the microstructure and enhance the mechanical properties of static and stress aged samples. The fine grained structure along with equiaxed and uniform grains were achieved for the stress aged samples, while bimodal structure with coarse grains was observed for the solution treated sample. It was shown that rolling and stress aging can form strong basal texture aligned with the normal direction. It was also observed that in solution treated sample few number of coarse precipitates were formed, while high density of fine precipitates was observed for the static aged sample. The stress aged sample possessed higher density of precipitates relative to the solution treated and static aged samples. The results obtained from the tensile tests proved that the mechanical properties of both static and stress aged samples were higher than that of the solution treated sample. While the tensile strength and elongation to failure of solution treated sample was 255 MPa and 11.2% respectively, the tensile response for best condition of static aged sample was improved up to 304 MPa and 25%. The rolling and stress aging processes under the load of 50 MPa for 3 hours improved the tensile strength of samples up to 353 MPa and ductility up to 12.5%. At -60℃, the mechanical response of solution treated sample is limited to strength of 262 MPa and ductility of 2.6%. The mechanical properties of stress aged sample are significantly improved at the same temperature up to strength of 338 MPa and ductility of 9.2%.