Effect of grain refining and Sr-modification interactions on the impact toughness of Al–Si–Mg cast alloys

• Impact properties of Sr-modified A356.2 alloys using various grain refiners.
• Addition of Ti and B greatly improves toughness of fully modified alloy.
• Highest toughness obtained for T6-alloys with Al–5%Ti–1%B and Al–10%Ti master alloys.
• Sr–B interaction may result in significant deterioration in impact properties.

The present work investigates the effects of various types of grain refiners on the impact properties of Sr-modified A356.2 alloys in both the as-cast and heated-treated conditions. The results showed that the addition of Ti and B greatly improves the alloy toughness, but only when the alloy was in a fully modified state; moreover, the right type of master alloy and addition levels must be used. The highest values of the total absorbed energy recorded for T6-tempered alloys were obtained using Al–5%Ti–1%B and Al–10%Ti master alloys in addition to 0.04%Ti. A significant deterioration in the impact properties is observed due to the Sr–B interaction (in some cases). The improvements in toughness may be attributed to the change in Si particle morphology as well as to the dissolution and fragmentation of a number of the intermetallics formed during the T6 temper.

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