Microstructures and Mechanical Properties of Al-Zn-Mg Alloy after Adding Al-5Ti-B Refiner and Al-2Zr-Sc Intermediate Alloy

Al-Zn-Mg alloy was refined with the single or compound addition of Al-2Zr-Sc intermediate alloy and Al-5Ti-B refiner. The microstructures and mechanical properties of as-cast Mg-Al-Zn alloys prepared under different refining conditions were studied. The results show that the grains were refined by single adding 0.4wt% Al-5Ti-B refiner or 0.4wt% Al-2Zr-Sc intermediate alloy, and the tensile strength was improved by Al₃(Sc,Zr) phases after the addition of 0.4wt% Al-2Zr-Sc intermediate alloy. The refining effects of grains was best after compound addition of 0.2wt% Al-5Ti-B and 0.2wt% Al-2Zr-Sc, compared with the alloy before adding, the average grain size of the alloy after compound addition was reduced by 20 μm, and tensile strength was increased by 32%, which was result of grain strengthening and dispersion strengthening. The second phase with long rod shape caused the elongation of the alloy after compound refining was lower than that of the alloy after single refining.