| 摘要 |
PROBLEM TO BE SOLVED: To contract and deform the member in the shape of bellows without generating crushing cracks in the case of being applied with the impact load of contraction or the static load of contraction in the direction of an extruding axis by forming it from a heat treated type aluminum alloy extruded material subjected to overaging treatment. SOLUTION: An Al-Mg-Si series Al alloy extruded material suitable from the viewpoints of strength, corrosion resistance and recycle ability is subjected to overaging treatment, e.g. under condition of 210 to 230 deg.C×150 to 240 min. In the case the maximum value of proof stress (σ0.2) obtd. by executing aging treatment is defined asσmax, it shall have the proof stress of (0.9 to 0.5)×σmax by overaging treatment. Particularly, in the case the Al alloy extruded material contains, by weight, 0.35 to 1.1% Mg, 0.5 to 1.3% Si, 0.15 to 0.7% Cu, 0.005 to 0.2% Ti and 0.06 to 0.2% Zr and contains one or more of 0.05 to 0.5% Mn and 0.05 to 1.5% Cr, its crushing and cracking resistance can be improved even by slight overaging treatment. As for its strength and the amt. of energy to be absorbed, the potential of the stock itself is not excessively sacrificed.
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