The formation of Sr6.33Mg16.67Si13 in magnesium alloy AM50 and its effect on mechanical properties

The increasing use of magnesium castings for automotive components and the number of newly developed alloys raise the question of suitable recycling processes. Remelting offers a high potential of energy saving and thereby improves the live cycle balance of magnesium components. Effective recycling processes are likely to involve the mixing of different alloys but little is known about the interaction of alloying elements. In order to approach this issue, the influence of strontium, silicon and calcium on phase formation and mechanical properties of magnesium alloy AM50 has been investigated. After strontium addition, X-ray diffraction demonstrated the formation of the Al4Sr and the Mg17Sr2 phases. However, after simultaneous alloying with strontium, silicon and calcium the ternary Zintl phase Sr6.33Mg16.67Si13 was detected. This phase forms preferably instead of Al4Sr, Mg17Sr2 and Mg2Si. Compared to the two strontium-containing phases, precipitates of the ternary Zintl phase exhibit a rather compact morphology. This results in a higher elongation-at-fracture under tensile stress.