MICROSTRUCTURE, MECHANICAL CHARACTERIZATION AND HOT TENSILE BEHAVIOUR OF AN AL-ZN-MG-ZR ALLOY

Two Al-Zn-Mg alloys (Zr modified and not) were investigated by optical microscopy, hardness and tensile tests. The alloys were solutionized (2h at 490 degrees C) and artificially aged at 130,160, 190 and 210 degrees C. Tensile tests were performed at room temperature on as-cast, solutionized and peak aged and the deformed samples annealed at 500 degrees C. Tensile tests at 250 degrees C-400 degrees C and 10(-5)s(-1) to 10(-3)s(-1) were run on as-cast alloys. For both the alloys at room temperature, the solutionized samples exhibited the best ductility, the peak aged the highest strength and the as-cast alloy the highest strain-hardening rate. Hot tensile behaviours of both alloys are similar. The higher average grain size of the Zr alloy does not lead to lower hardness and peak stresses during room temperature (RT) tensile tests. Recrystallization of Zr-modified alloy is incomplete and not homogeneous as compared with unmodified alloy.