Individual Contribution of Zn and Ca on Age-Hardenability and Formability of Zn-Based Magnesium Alloy Sheet

This paper reports on the dilemma of the strength and forming behavior of magnesium alloy sheets due to hot rolling and precipitation aging as an obstacle for property adjustment. The effect of the Zn content on the age-hardenability and formability of Mg-Zn-Al-Ca-Mn sheets was investigated. Sheets of two alloys with 2 or 4 wt.% Zn, respectively, were produced by casting and subsequent hot rolling and their microstructure development, precipitation behavior and formability were examined. With higher Zn content the age-hardenability was increased, but at the same time the formability of the sheet decreased, concurrent to the basal-type texture development during rolling. On the other hand, the sheet containing a lower amount of Zn exhibited a weak rolling texture and rather high formability but low age-hardenability. The addition of a larger amount of Zn improved the age-hardenability through the formation of β1' and β2' phases. The basal texture was exhibited due to the consumption of solute Ca due to the formation of the Ca₂Mg₆Zn₃ phase. This study suggests that this contradictory exhibition of the age-hardenability and formability of Ca-containing and Zn-based alloy sheets requires a strategical approach in alloy and process design, which allows tailoring the alloying elements and processing for the respective purpose.