Effect of solution and modification treatments on the crack propagation behaviour of Al-7Si alloy under resonant vibration

In order to investigate the influence of solution treatment and modification treatment on the crack propagation behaviour of Al-7Si alloy under resonant vibration, the unmodified and Sr-modified materials were tested. The experimental results indicate that the resistance to crack propagation is improved after solution treatment for both the unmodified and modified alloys. The improvement of cracking resistance of unmodified alloy is due to the change in the cracking paths from broken-through particles to particle/matrix interfaces. The unmodified alloy possesses better cracking resistance than does the modified alloy after solution treating at 535°C for 2 hours. On the other hand, the modification treatment shows no obvious improvement to cracking resistance. In the modified alloy, the crack paths of the as-cast and solution-treated specimens both preferentially progress toward the interdendritic zones. The as-cast alloy shows this trend more strongly and hence its cracking trajectory is more meandering and branching.