How to Reduce Porosity Defects in Cast Al-Si Alloys

    Hello everyone, I'm Venda from China. I've been working in the lost wax investment casting industry for over 20 years. Today, I'd like to briefly discuss how to reduce porosity in cast Al-Si alloys. If you have any insights, please leave me a message. My WhatsApp account is: +8618562112686.

Sr modification is a key process in the casting of hypoeutectic Al-Si alloys. However, Sr modification can increase porosity in castings. This is partly because the introduction of Sr increases the Al-Si alloy's tendency to absorb hydrogen. Furthermore, Sr reduces the melt's surface tension, facilitating the formation of hydrogen pores. In other words, even if the melt's gas absorption does not increase, the presence of Sr increases its tendency to form pores. Therefore, reducing gas absorption through melt degassing and other measures can only partially reduce porosity. Effective reduction in porosity requires the following measures:

1. Reduce the amount of Sr added. To fully modify Si, Sr is generally added at a level of at least 200 ppm during production. In fact, an Sr content of at least 100 ppm in the melt is sufficient for Si modification. 2. Appropriately accelerate the solidification rate. When the solidification rate is accelerated, hydrogen in the melt has less time to precipitate during solidification, thus preventing the formation of hydrogen pores. However, this faster solidification rate shortens the feeding time, potentially leading to shrinkage defects. Therefore, it is necessary to strengthen feeding by enlarging the riser, for example.

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