An AZ91 alloy was preparded by a gravity casting process with either constant grain size or constant cooling rate. The as-cast alloys show good mechanical properties with decreasing dendrite arm spacing (DAS) or grain size. These phenomena are possibly explaned by the fact that cracks do not easily propagate in the brittle eutectic Mg₁₇Al₁₂ compounds due to the fine compounds. The ultimate tensile strength (UTS), 0.2% proof stress (PS) and elongation (E_f) at fracture of the T6 treated alloys increase with decreasing grain size. But the UTS and E_f of the alloy remain almost constant with decreasing DAS, while the PS increases with decreasing DAS. These phenomena in the T6 treated alloys are explained by assuming that (1) the stress concentration at a grain boundary is higher with larger grain size, (2) the density of grain boundaries which act as obstacles during crack propagation is higher with smaller grain size and (3) the homogenization is easily achieved in a shorter solution heat-treatment time with a small DAS.

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In order to improve the drilling performance of titanium alloy (Ti–6Al–4V), drilling under high pressure supply of coolant has been investigated. High pressure supply (7 MPa) and conventional supply of coolant are compared mainly on tool wear in drilling by drill with oil holes in its lands. To make clear the causal relation between tool wear and cutting conditions, cutting forces and cutting temperature are measured. The results obtained are as follows; (1) High pressure supply of coolant is effective on drill wear in high cutting speed that drill wear increases significantly under conventional supply. (2) Critical cutting speed is determined from cutting temperature that hardness of tool material decreases remarkably. (3) Under high pressure supply of coolant, cutting temperature does not increase remarkably even in drilling a deep hole because major cutting edges are cooled and chips are ejected smoothly. (4) At low cutting speed and low feed rate, wear of drill is smaller under conventional supply of coolant. (5) It is important to improve the rigidity on drilling system when used at high pressure supply of coolant.

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A new incremental process in which a tool deforms an aluminum blank to its circular tool-envelope surface was employed in order to measure the incremental forming limit. The forming limits were determined by the occurrence of rupture in the direction of tool travel. The limit strains for incremental forming were strongly dependent on the value of incremental tool-path-pitch Δh; the limit strains increased with decreasing Δh. Similar effects of Δh on the limit strain were also obtained under other experimental conditions. Thus, the incremental tool-path-pitch Δh had a major influence on the forming limit. Furthermore, the forming limits were controlled by the history of incremental strain, i.e., strain wave-form, strain range and number of strain cycles.

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In order to resolve the chip disposal problem during drilling, the chip formation process during intermittently decelerated feed drilling is considered. Long continuous chips are formed in conventional drilling. As a prelude to obtaining the necessary basic data for control the chip shape, the relation between cutting variables of intermittently decelerated feed drilling and chip shape was investigated using 2017 aluminum alloy that entails difficult chip disposal, (1) Chip breakage increases at a deceleration ratio that gives rise to large variations in shear angle during drilling. (2) The amplitude of the dynamic component of thrust and torque in intermittently decelerated feed drilling is greatly influenced by the deceleration ratio. (3) At an appropriate deceleration ratio during intermittently decelerated feed drilling, chips formed break into suitable lengths thus, making it an effective drilling method for achieving good chip disposal.

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The effects of Li and Si contents on the solidified and heat treated structures of Al–2.5~5 mass%Li–O.7~7 mass%Si–1 mass%Mg alloys cast into metal and sand molds were investigated by scanning electron microscopy, specific heat curve measurement, X-ray diffraction and micro-vickers hardness measurement. AlLiSi compounds crystallize as primary and eutectic phases and disperse at the inter-dendrite arm, and they remaind intact after solution treatment at 803 K for 36 ks. The crystallization of primary and eutectic Si phases, and Mg₂Si phases were not observed. The morphology of the AlLiSi phase is triangular plate-like in the alloys contained more than 3 mass%Si, is needle-like in the alloys contained 1~3 mass%Si and changed to small rod-like in the alloys contained less than 1 mass%Si. By the amount decrease in the solubility of Li in the matrix the crystallization of AlLiSi phase decreases and brings the decrease or retardation in age hardening by δ' (Al₃Li) precipitation. The mechanical strength becomes higher with decreasing the amount of AlLiSi phase and δ (AlLi) equilibrium phase.

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In order to improve the surface quality of ingots fabricated by an electromagnetic casting, a header which restrains the growth and the movement of oxide films was set on the side free surface of a molten metal constrained by an electromagnetic force. The shapes and the materials of the header were examined under aluminum alloy castings. It is noticed that an electrically conducting graphite header provided the better surface qualities regarding the roughness and the thickness of oxide films than an electrically insulating refractory header did. The electromagnetic force and the velocity distribution in a molten metal are numerically calculated and the surface qualities obtained in the experiment are discussed in relation with the numerical results. It is found that a contacting pressure between a molten metal and the header is larger in graphite header than that in the refractory one and the molten metal just below the side free surface flows upward in the graphite header and downward in the refractory one.

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