Abstract
The effect of heat treatment condition on non-Cu AA7021 alloy was investigated with respect to mechanical properties and very high cycle fatigue behavior. With a focus on the influence of heat treatment, AA7021 alloy was solution heat-treated at 470 °C for 4 h and aged at 124 °C. Comparing the results of solution-treated and peak-aged AA7021 alloy shows a significant increase in Vickers hardness and tensile strength. The hardness of AA7021 alloy was increased by 65% after aging treatment, and both tensile strength and yield strength were increased by 50~80 MPa in each case. In particular, this paper investigated the very high cycle fatigue behavior of AA7021 alloy with the ultrasonic fatigue testing method using a resonance frequency of 20 kHz. The fatigue results showed that the stress amplitude of peak-aged AA7021 alloy was about 50 MPa higher than the solution-treated alloy at the same fatigue cycles. Furthermore, it was confirmed that the size of the crack initiation site was larger after peak aging than after solution treatment.
Highlights
The effect of heat treatment condition on non-Cu AA7021 alloy was investigated with respect to mechanical properties and very high cycle fatigue behavior
The average hardness of AA7021 alloy before heat treatment was 105 HV, and this decreased to 98 HV after solution treatment
The average hardness of AA7021 gradually increased after aging treatment, and it showed the highest value of 148 HV after 32 h of aging
Summary
The effect of heat treatment condition on non-Cu AA7021 alloy was investigated with respect to mechanical properties and very high cycle fatigue behavior. A typical high-strength aluminum alloy often used in industrial environments is AA7075 alloy; when properties such as extrusion workability, weldability, and corrosion resistance are required at the same time, the non-Cu-containing AA7N01 alloy is used [2,3,4]. Such AA7xxx alloys with superior properties have been used in structural materials, aircraft, automobile parts, and are used in portable electronic devices [5]. Tensile testing and very high cycle fatigue testing were conducted to evaluate tensile properties, strain energy densities and high-cycle fatigue behaviors
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