Effects of heat treatment and minor additional elements Cr or Zr on mechanical and SCC properties of 7075 based cast alloys fabricated with a newly developed rheocast method were investigated. SCC tests were conducted by SSRT slow strain rate tensile technique using a round bar tensile specimen under a constant strain rate 8.3ϫ10 Ϫ7 /s in 3.5%NaCl aerated solution. Similarly with a rolled alloy 7075, the rheocast alloy with temper of underaging or peak-aging T6 showed a high susceptibility to SCC, while the alloy with temper of overaging, T73 or T77 exhibited a less elongation in tensile property, although together with an improved resistance to SCC. On the other hand, the alloy direct-quenched into an oil bath at 433 K from solution temperature, followed by aging for 86.4 ks, represented a superior combination among strength, elongation and SCC resistance, and the alloy with 0.2 mass% Cr addition showed a more improved combination. The improvement was attributed to a repression of hydrogen embrittlement caused by coarsening of precipitates in gain matrix and along grain boundary, and further by a relief for planar slip due to fine distribution of Cr dispersoides within grains.
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