Grain size of primary silicon and its cooling rate dependency were first studied on hyper eutectic Al-20%Si alloy which had been prepared with various mold materials. Then, the effects of single addition (about 0.2at.%) of about 30 sorts of the 3rd elements on the grain size of primary silicon and its cooling rate dependency were fully examined on wedge-shaped samples cast with pure copper mold. The effects of the addition amounts of effective elements and the double addtion of the said elements were also studied.
The main results obtained were as follows:
(1) The grain size of primary silicon was expressed by almost hyperbolic relation with the cooling rate. When the cooling rate was in the range of higher than 20°C/sec, the grain size and its cooling rate dependency decreased; but, they sharply increased in the range of lower than 10°C/sec.
(2) Relating to the cooling rate dependency, Li, Na, Cd, B, Sn, Pb, V, Sb, Te, Ni, and rate earths (Larich) showed almost the same tendency as the case of no addition; Cu, Ag, Zn, In, Ti, Zr, Bi, and Mn showed the tendency of larger cooling rate dependency; while, Be, Mg, Ca, P, Cr, Se, and rare earths (Ce-rich) showed the tendency of smaller cooling rate dependency.
(3) The most effective element for the decrease of cooling rate dependency was found to be phosphorus. The double addition of more effective elements was not so effective as the single addition of phosphorus.
(4) Most elements, giving the decrease of cooling rate dependency also gave the decrease of grain size.
(5) Eutectic matrices of these alloys were improved in all cases, except the additions of Cu, Ag, Be, Sn, Pb, V, P, and Mn.

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The Al-12.2% Si and Al-12.2% Si-0.8% Mg alloys were prepared with metallic molds. The changes of their properties such as hardness, mean free path between silicon particles, and mean radius of silicon particles were studied after annealed at 400-500°C to determine the working conditions of the alloys. Some mechanical properties of these sheets were examined after hot-rolled and finally cold-rolled to 0.5mm in thickness.
The main results obtained were as follows:
(1) The hot and cold working of these alloys were made possible by the increase of mean free path and mean radius of silicon particles, due to an appropriate annealing at about 500°C for 3hr. The intermediate annealing at about 300-350°C for 1hr. was required during the process of cold-rolling of thes alloys.
(2) The mechanical properties of the above rolled sheets were superior to those of any other practical alloys of the same type. For example, tensile strength, elongation, and hardness of cold-rolled Al-l2.2% Si sheet were 24kg/mm², 3%, and Hv 66, respectively. Those of Al-12.2% Si-0.8% Mg sheet were 25kg/mm², 14%, and Hv 55 in solution heat-treated state, respectively; and 37kg/mm², 8%, and Hv 107 in T6 treated state, respectively.
(3) Microstructure of the both rolled alloys showed the almost uniform dispersion of silicon particles, but no rupture of particles during working.

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The machinability relating to cutting resistance, surface roughness, built-up edge, treatment of chips, drilling time, etc. was discussed on three sorts of alloys now under development based on Al-Zn-Mg system as cast and after natural aging for two weeks. Furthermore, the machinability was pursued in the same way for four sorts of new alloys, which had been prepared with different chemical compositions for the use of pressure die casting.
As the results, the alloys now under development showed low cutting resistance and rather rough surface as cast; but, after natural aging for two weeks, they showed more improved surface though accompanied with slightly higher cutting resistance. However, the new alloys as cast showed much higher cutting resistance than the former alloys, but after natural aging for two weeks, the resistance was reduced to be as low as that of the former (after aging) and the surface was more improved than that of the former (after aging). The treatment of chips seemed to be left out of considerations in any case.

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High speed cutting tests were conducted on the metallic mold castings and low pressure castings for the specimens of as cast (F material) and heat-treated (T-6 material) for the purpose of examining the machinability of aluminum casting alloy AC2B. The following results were obtained.
It seemed that these materials showed lower cutting resistance as compared with other aluminium alloys. The resistance of low pressure castings was slightly lower than that of metallic mold castings, and the resistance of T-6 materials was higher than that of F materials in any case. There were no distinct differences in the growth of built-up edge, surface roughness, formation of chips, etc. between the both castings, but some differences between the both materials in any case. For example, built-up edge was clearly recognized on F material, but not T-6 material; trace marks by feeding tool were distinct on the finished surface of T-6 material which was bright, but a very rough and lustreless surface was apt to be shown on F material. In addition, there would be some troubles for treatment of chips on F material. In case of large side rake angle, macrostructure appeared on the finished cutting surface of T-6 treated low pressure castings.

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Most of aluminum alloy castings belong to the same system as wrought aluminum, but the former are superior to the latter in strength and castability by the effects of larger amounts of additional elements. Therefore, the variation of mechanical properties, etc. is larger in the former as compared with that of the latter. It was considered that machinability of the former was considerably distinguished from that of the latter due to their rough structure and segregation or crystal precipitation peculiar to their cast structure. It was also assumed that optimum machining conditions of the former were varied with the great change of structure by cooling or heat treatment. Accordingly, it would be essential to discuss the machinability of aluminum alloy castings from a new point of view apart from wrought materials. The effects of the content of an additional element, or one of Si, Cu, Mg, etc., on the machinability of the alloy castings are pursued in this paper. Further, there are discussed on the machinability of the products obtained by pressure die casting or low pressure die casting different from ordinary gravity casting.

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