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In order to develop large-scale (100 mm in diameter) Mg-Zn-Y alloys with high strength beyond that of 4032-T6 alloy, we considered a novel casting process to produce large ingots with homogeneous microstructure, and investigated the mechanical properties of the extruded alloys. First, ingots (335 mm in diameter and 850 mm in height) were produced by a novel stir casting process in the ingot case. Then large-scale extruded alloys (100 mm in diameter) were prepared with an extrusion ratio of 10. The Mg-Zn-Y alloys exhibited higher yield and fatigue strengths than those of 4032-T6 aluminum alloy. The yield strengths of the aluminum alloy decreased drastically above 473 K, whereas those of the Mg-Zn-Y alloys did not. It is noteworthy that the yield strength (274 MPa) and fatigue strength (100 MPa) of the Mg-Zn-Y alloys at 473 K were about 1.3 and 1.2 times respectively as high as those of aluminum alloys.

A small four-stroke engine capable of all positional operation has been developed. The engine for hand held equipment provides easy maneuverability like two-stroke engines which are dominated in the small engine market. The developed technologies include the following items. ① 360° all positional operation by adopting a new lubrication system. ② Light-weight with a thin uni-block cylinder, etc. ③ Normal operation at more than 10,000 rpm and at low and medium revolution range are combined by high output with a wide torque band. Equally easy handling and better workability compared with the conventional two-stroke engines are achieved. In addition, better starting reliability, drastically improved emission, and half-reduction of running costs are also confirmed.