研究論文
ADC12合金ダイカストの熱処理時におけるひずみ挙動とそのメカニズム
2017 年 89 巻 3 号 p. 111-118
詳細
2017 年 89 巻 3 号 p. 111-118
To ensure dimensional precision in various service environments, this study investigated the strain variation of JIS ADC12 aluminum alloy die castings by heat treatment and its relation with the strain (hereinafter, growth) arising from the precipitation of silicon, copper, and magnesium.
Expansion strain exceeding 0.1% was produced in a JIS ADC12 aluminum alloy die casting by heat treatment. Simultaneously, the half-width angles of the X-ray diffraction (XRD) peaks of the aluminum phase in the die casting decreased. Silicon, copper, and magnesium concentrated phases appeared in the aluminum phase after heat treatment. Consequently, the decrease in the half-width angles can be regarded as a result of the improved crystallinity of the aluminum phase because of the relaxation of the lattice strain by the precipitation of silicon, copper, and magnesium. That is to say, the strain variation of the ADC12 alloy die casting by the heat treatment is attributable to the precipitation of silicon, copper, and magnesium from the supersaturated aluminum phase. To verify the above relation quantitatively, growth attributable to the precipitation of silicon, copper, and magnesium from the aluminum phase and the transformation of the precipitated metastable Cu-Al compounds was estimated theoretically and compared with the measured strain variation yielded by heat treatment of the ADC12 alloy die casting. Results confirmed that the strain variation of the ADC12 alloy die casting by heat treatment corresponded fairly well to the growth arising from the precipitation of silicon, copper, and magnesium out of the aluminum phase and the transformation of the precipitated metastable Cu-Al compounds. Results also show that silicon, copper and magnesium precipitated at an early stage of heat treatment and that the silicon precipitation contributed mostly to the growth. The precipitated metastable Cu-Al compound, θ", was found transformed to another metastable compound, θ', and stable compound, θ, sequentially, thereby giving some expansion and contraction growth.
