Effect of Sc and Zn Additions on Microstructure and Hot Formability of Al-Mg Sheet Alloys

Trace elements of Sc or Zn were added to Al-Mg sheet alloys. Microstructural examination showed that the Sc addition greatly refined the grain size, especially in the Zn-containing alloy where large amounts of subgrains and fine grains were formed. Meanwhile, a number of large primary intermetallic particles formed in the Sc-adding alloys. In order to evaluate the high-temperature formability, warm tensile tests were carried out at temperatures ranging from 275 °C to 350 °C and at strain rates of 0.015 to 1.5 s. The test results showed that, in the alloys with the single addition of Zn or Sc, Zn slightly increased the flow stress but decreased the ductility and Sc worsened both the flow stress and the ductility. However, in the alloy with the combined addition of Zn and Sc, the flow stress was significantly increased at almost all testing conditions and the ductility was also increased at a higher temperature of 350 °C and lower strain rate of 0.015 s. The results of superplastic tensile tests and biaxial stretch tests demonstrated that the alloy with both Zn and Sc additions exhibited good high-temperature formability. The effect of Zn and Sc additions on the microstructure and the hot formability is discussed