Abstract:The effect of Er on the microhardness and precipitation behavior of the heat-treated Al-Si-Mg alloy was investigated by microhardness tester and TEM. As a comparison, the influence of natural aging was also studied. It is shown that the thermal stability of the over-aged Al-Si-Mg-Er alloy is highly related to the average size of the precipitates. The average size of β'''''''' precipitates in Al-Si-Mg-Er alloy is smaller than that in Al-Si-Mg alloy, and the distribution is more localized under condition of without introducing natural aging. However, when natural aging is introduced before artificial aging, the Al-Si-Mg-Er alloy has similar average size and distribution of precipitates with the Al-Si-Mg alloy, resulting in similar mechanical properties. The effect of Er on the precipitation kinetics in the alloy was also discussed in detail to explain these phenomena.

Key words: Al-Si-Mg alloy; Er; natural aging; precipitate; thermal stability