Improve Properties without Downsides

Is it realistic to improve properties without changing anything? No! It would be best if you changed something to trigger a different outcome. Take a critical specification like the Volkswagen norm TL133 as an example. It is an AlSi7MnMg alloy. When you look at the spec sheet, you see pretty large windows for each element. So, to have a consistent production output, you need to narrow the range internally.

There is a vast difference in the mechanical properties and the castability between 6,0 and 7,5% Silicon. The higher silicon content gives you better castability because of the smaller solidification window. However, the higher silicon content forms more eutectic silicon needles, which increase strength as a trade-off for elongation. At 6,0% silicon, you get worse castability but higher elongation because of the fewer silicon needles. Strontium helps modify the needles to be less pointy. Here, it is quite easy; the maximum allowance of Strontium helps the best because it burns off in the holding furnace.

The iron content is limited to 0,20%. Low iron content in the aluminium alloy leads to a stronger chemical attack on the tool steel. To reduce that tendency, Manganese is added to the alloy. Manganese is similar to iron and reduces its solubility in the liquid alloy. But Manganese forms precipitates that reduce the ductility of the casting. Also, the chemical attack on the tool steel depends on the silicon content. A lower silicon content results in a higher liquidus point and, therefore, a longer contact time of the liquid aluminium with the tool steel. In addition, the casting temperature impacts the tool wear, too. A lower temperature helps with tool wear. But it gets increasingly challenging for the melt fronts to recombine at the end of the filling with cooler melts.

In small amounts, Magnesium and Zinc are soluble in the aluminium matrix. Both elements increase the strength of the casting while reducing its elongation. The effect on elongation is quite imminent. Natural aging, a heat treatment, or the paint-bake cycle impact this trade-off significantly.

There are also impurities in other elements that are typically capped 0,05%. Still, they impact the mechanical performance of the later casting. The Calcium content is mentioned separately. Reducing the amount of impurities is expensive.

As you can see, the customer specifications must be narrowed down to an internal specification that fits your product portfolio and production needs. But where should you place your production window? It’s a multidimensional optimization process that takes a lot of time. Also, smaller chemical composition windows are harder to maintain and more expensive to order.

Simulations with physics-based models complemented by AI can significantly reduce trial time and costs. Let’s start a conversation in the free Consultation Call about optimizing your production and delivering higher-quality castings to your customers! Customer satisfaction is the most essential thing, and it outweighs all downsides!