When you think of heat treatment, I wonder what type of metal you associate it with? Aluminium is probably not the first metal that springs to mind. Why? Because it is thought of as being a soft metal. But there are certain, specific alloys which respond incredibly well to heat treatment, in fact, they actually respond in almost the same way as steel and iron. So, what are the specific types of aluminium alloys? They are aluminium alloys containing copper, zinc, or a blend of magnesium and silicon which enable them to respond well to the heat treatment process. Be aware that pure aluminium and aluminium alloyed with manganese or magnesium does not work under heat treatment. Therefore, when referring to the heat treatment process during this article, it is aluminium alloys containing copper, zinc or a blend of magnesium and silicon that is being referred to.
Aluminium alloys come in to contact with the mold via their outside edge first, which forms a layer or skin of aluminium crystals, which are called grains. This occurs when aluminium alloys are being cast. They cool from the outside in, with the elements of the alloy precipitating which locks crystals in regionally. This is how some areas become hard and some remain soft. To even this imbalance out, we need homogenizing, so that redistribution of the precipitation can occur. This means that the temperature needs to be taken to just below melting point which is between 900 and 1000 degrees farenheit. Having reached the homogenizing temperature, the component is left to cool slowly, so that the internal structures uniformity is reached.
Annealing Aluminium Alloys
If you then require you aluminium alloys to be shaped, you will then require another process which is known as annealing. The alloys must be heated once again to 570°F to 770°F for anywhere between thirty minutes to three hours, depending on the alloys composition and the component part. Unlike the heat treatment or homogenising processes, the cooling process post annealing is not a critical factor in this process.