알루미늄 7050 합금의 대기 및 3. 5 % NaCl 수용액에서의 파괴거동에 관한 연구

This research investigates the effects of heat treatment, displacement rate and orientation on fracture behavior of precipitation hardened Al-Zn-Mg-Cu alloy 7050 in air and aqueous NaCl solution utilizing fracture mechanics R curve concept. It was found that K_(th) value of Al 7050 increased with decreasing displacement rate from 10^(-3)㎜/sec to 10^(-5)㎜/sec, possibly due to the enhanced homogeneous deformation and reduced stress concentration at the microvoid nucleation sites. In 3.5% NaCl solution, on the other hand, the K_(th) value increased with the displacement rate down to 10^(-4)㎜/sec, and decreased with further decreasing displacement rate, demonstrating that the environmental effects become dominant at lower displacement rates. T73 tempered Al 7050 showed reduced resistance to fracture compared to the T6 counterpart as a result of coarse precipitates formation and large grain size. It was also found that Al 7050-T73 has superior stress corrosion cracking (SCC) resistance to Al 7075 in 3.5% NaCl solution. Constant displacement rate test method for K_(ISCC) and da/dt measurements requires extremely slow displacement rate for high SCC resistant alloys like Al 7050. (Received October 8, 1997)