Abstract
This report has been prepared on the basis of the statistical data on hard spots in die-cast products of aluminium alloy for the past several years.
Their external appearance was observed and compared with their microscopic structures and hardness obtained through the experimental works. As the result of the above-said study, it was found out that the hard spots could be classified into some types from their external appearances.
Besides the above, chemical analysis was also made on the non-metallic hard spots, alloy slags (oxides) and altered bricks. With respect to the non-metallic hard spots, the following results were obtained.
1) The major components of the non-metallic hard spots are Al2O3, SiO2 and Fe2O3 and Na2O, MgO, TiO2, Cu and some others are also contained through slightly.
2) The composition of the hard spots made of altered brick (which is made by being attacked by molten aluminium alloy) and of aluminium alloy slags are different from that of the non-metallic hard spots in the quantity of the contents of the major components.
3) Accordingly, the non-metallic hard spots are not the altered brick alloy slags themselves, although it is considered that they may be one of the factors for the formation of non-metallic hard spots.
