Effects of Annealing on Mechanical and Corrosion Properties of As-Extruded NQZ310K Alloy

The as-extruded NQZ310K (Mg-3.0Nd-1.0Ag-0.2Zn-0.4Zr, mass fraction) alloy was annealed at 300, 350, 400, 450, and 500 °C, respectively. Microstructures of the alloy were observed by an optical microscope and a scanning electron microscope equipped with an energy-dispersive X-ray spectroscope. Ambient mechanical properties were evaluated by tensile tests and nanoindentation tests, and corrosion behavior in simulated body fluid was measured by immersion test. The results show that both matrix grains and precipitates grow up with increasing annealing temperature, and the amount of the precipitates is reduced. The yield strength of the alloy under the as-extruded condition and annealed at 300 and 350 °C is 297, 313, and 298 MPa, and the ultimate tensile strength of it is 327 , 328 , and 315 MPa, respectively, indicating high yield ratio. After annealing at 400, 450, and 500 °C, the yield strength reduces faster than the ultimate tensile strength, resulting in the yield ratio decrease from 0.95 to 0.61, and the elongation improves significantly from 12.3 to 25.5%. The alloy annealed at 350 °C presents the lowest corrosion rate, and then the corrosion resistance of the alloy decreases with increasing annealing temperature. The effects of annealing on microstructure, mechanical and corrosion properties of the as-extruded NQZ310K alloy were also compared with the properties of solution treated alloy.