鋳造用Al-Si-Mg合金の機械的性質並びに応力腐食割れに及ぼす亜鉛，銅の影響

概要

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The effect of addition of 0.5-5%Zn and 1.3%Cu on the mechanical properties and stress corrosion cracking of Al-5%Si-0.5%Mg alloy casting was investigated. Also examined was the effect of microporosity on the stress corrosion cracking and furthermore the susceptibility to stress corrosion cracking between A7075 alloy and Al-5%Si-0.5%Mg-2%Zn alloy were compared. Stress corrosion cracking test was conducted in 5.0%NaCl solution at 30±1°C under constant strain (giving 100% strain corresponding to 0.2% proof stress of each alloy). A remarkable improvement in tensile strength was achieved by adding to Al-5%Si-0.5%Mg alloy and 3%Zn to Al-5%Si-0.5%Mg-1.3%Cu alloy. It was 32.5kg/mm2 for the former and 36.4kg/mm2 for the latter. When the Zn content was increased up to 5% in Al-5%Si-0.5%Mg alloy, the susceptibility to stress corrosion cracking of Al-5%Si-0.5%Mg alloy containing 0.5-5%Zn also slightly increased by 1.3%Cu addition. On the basis of results by E.P.M.A., it was confirmed that stress corrosion cracking ran along the grain bounday where eutectic Si were found, but was not caused by the segregation of the solute elements i.e. Zn, Cu, Si and Mg. In Al-5%Si-0.5%Mg alloy containing up to 2%Zn, the degree of microporosity had greater effect on the susceptibility to stress corrosion than the Zn content. The susceptibility to stress corrosion of Al-5%Si-0.5Mg-2%Zn alloy was about one tenth of A7075 alloy.
Japan Foundry Engineering Societyの論文