Abstract
It is generally known that there are three kinds in hard-spots which appears in aluminium die castings. But, another kind of hard-spot was found, which is not observed in micro-structure. This hard spot is named here as "Hardspot of Segregation, because alloying elements are concentrated in it.
Therefore, this hard-spot shows aluminium alloy structure. It generally appears on the overflow-side (riser) of die casting.
From observation of micro-structure of various kinds of hard-spots, the following results were obtained:
(1) The structure of hard-spot is fine and chilled. It seems that alloying elements are concentrated in it.
(2) The micro-structures of hard-spots are classified into five kinds. One of them is extremely fine compared with others.
(3) Some of such structure are homogeneous and some are unhomogeneous.
(4) Boundaries of hard-spots are also classified into several kinds. It is considered they are different according to the conditions under which the segregation takes place.
(5) Grains of alloying elements contained in the structure of hard-spots are extremely fine.
