การหาค่าพารามิเตอร์ที่เหมาะสมที่สุดของกระบวนการรีดลึกบนแนวเชื่อมแรงเสียดทานแบบกวนของวัสดุต่างประเภทระหว่างโลหะผสมอลูมิเนียม 6061-T6 และ 7075-T651

Abstract

The main purpose of this research was to enhance the mechanical properties of friction stir welds (FSW) in the dissimilar aluminum alloys 6061-T6 and 7075-T651. The welded workpiece has tensile residual stress due to the influence of the thermal conductivity of dissimilar materials, resulting in crack initiation and less fatigue strength. The experiment started from the FSW process using the 2k full factorial with the response surface methodology (RSM) and central composite design (CCD) to investigate three factors: rotation speed, feed rate and type of stirring tool. The experiment found that the optimal values were a rotation speed of 979 rev/min and a feed rate of 65 mm/min, and any type of stirring tool can be used. Then, the post-weld heat treatment process (PWHT) at 530 ◦C for 4 hours and 140 ◦C for 6 hours was applied. Following this, the 2k full factorial was used to investigate four factors involved in the deep rolling process (DR): deep rolling pressure, deep rolling speed, deep rolling offset and deep rolling direction. The experiment found that the optimal values were a deep rolling pressure of 300 bar and deep rolling offset of 0.2 mm; the deep rolling speed and deep rolling direction can use any value. Moreover, mechanical property testing was performed with a sequence of four design types of workpieces: FSW, FSW-PWHT, FSW-DR, and FSW-PWHT-DR. It was found that the FSW-PWHT-DR workpiece had an increase in tensile strength of up to 26.29% and increase in fatigue life of up to 129.47% when compared with the FSW workpieces