Effect of Alloying by Transitional Refractory Metals on the Microstructure and Thermal Stability of AI-5Zn-3Mg Alloys

摘要

Effect of alloying by transitional refractory metals (TM) on the structure and properties of the Al-Zn-Mg system alloys, made by different methods, is investigated. It is ascertained that strength of the especially cast alloys (CIA) is increased by scandium and zirconium alloying, due to the modificating action of scandium, inhibiting the recryctallization and precipitation of fine-grained coherent with the matrix Al_3(Sc_(1-x) Zr_x) phase; in less degree it tells on alloys, made by powder metallurgy technologies (P/M), in which the ultra-high cooling rate of melt atomized by high-pressure water plays a basic role in forming of the fine-grained structure. P/M semi-product both of the base composition AI-5Zn-3Mg and alloys without scandium are not recrystallized at the technological heatings up to 500 °C, while C/A alloys similar in composition are recrystallized already on the hot extrusion stage at 400-450 °C. The most high strength among the P/M alloys with scandium the Al-5Zn-3Mg-0.5Mn-0.7Zr-0.3Sc alloy showed of UTS=651 MPa and YS=596 MPa and among the P/M alloys without scandium the Al-5Zn-3Mg-0.85Zr-0.22Cr-0.17Ni-0.15Ti alloy showed the UTS=618 MPa and YS=553 MPa. Researches showed that at cooling rate of melt 10-10~6 K/s total content of transitional refractory metals must not exceed 1.5-1.7 wt% and total content (Zn+Mg) to 8wt% at correlation of Zn and Mg 5:3.