Improvement of strength-ductility balance and corrosion resistance in as-extruded Mg-Gd-Zn-Zr alloys by Zn/Gd ratio

Abstract

Three kinds of high-performance as-extruded Mg-Gd-Zn-Zr alloys were successfully prepared by controlling Zn and Gd contents and atomic ratio. The microstructure, mechanical properties and corrosion resistance of the three alloys were studied by optical microscope (OM), scanning electron microscope (SEM), X-ray diffractometer (XRD), electron backscattering diffraction (EBSD), tensile-compressive experiment and electrochemical experiment. The results showed that the coarse grains and continuous second phase of as-cast alloys were refined and broken after hot extrusion, and the main components were α-Mg, W–Mg3Gd2Zn3, I–Mg3Zn6Gd and MgZn2 phases. The mechanical properties and corrosion resistance tests revealed that the as-extruded GZ22 alloy had the highest ultimate tensile strength (UTS) of 362 ± 6 MPa and the lowest corrosion rate of 0.94 mm/year, which was attributed to the fine grains and a small amount of dispersed second phase. The strength of as-extruded GZ56 alloy decreased due to excessive hard and brittle W-phase. Meanwhile, a large amount of second phase content made the alloy had the lowest corrosion resistance. In addition, the as-extruded GZ26 alloy with high Zn/Gd atomic ratio had good comprehensive mechanical properties, and its UTS and elongation (EL) were 332 ± 3 MPa and 24.5 ± 0.6%, respectively. The unique feature of this alloy was that weak texture intensity led to good tension-compression yield symmetry, and its corrosion resistance was second only to that of the as-extruded GZ22 alloy.