ALUMINUM ALLOY HOLLOW SHAPED MEMBER EXCELLENT IN FATIGUE STRENGTH AND METHOD FOR MANUFACTURING THE SAME, AND SWING ARM FOR MOTORCYCLE

摘要

PROBLEM TO BE SOLVED: To provide an aluminum alloy hollow shaped member excellent in a fatigue strength and a method for manufacturing the same, and a swing arm for motorcycles.

SOLUTION: The aluminum alloy hollow shaped member consisting of an Al-Zn-Mg based aluminum alloy has a compressive residual stress in an outer surface of the hollow shaped member. Further, there exists no coarse recrystallized grain with a size of more than 500 μm in the whole area in the cross-section. The extruded tube consisting of the Al-Zn-Mg based aluminum alloy is subjected to a solution treatment by retaining it at a temperature of 350-480°C for one minute or more, a quenching treatment immediately thereafter, a hydro-forming at a maximum value of a circumferential length increase rate of 50% or less within two hours after the quenching treatment, and then an artificial aging treatment at a temperature of 90-160°C for 4-30 hours.

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