Heat treatment of ultrahigh strength 7A36 aluminum alloy extruded tube

Abstract

The single-stage & two-stage solution and the single aging-tensile property curves at 110-135 ℃ were studied by using the 7A36 aluminum alloy extruded tube of ϕ250 mm×20 mm and ϕ340 mm×30 mm under industrial production conditions. The optimal heat treatment was adopted to compare the tensile properties of two kinds of aluminum alloy extruded tube.The phase transition temperature was measured by DSC, and the microstructure and tensile fracture were observed by OM, SEM and TEM.The results show that the tensile strength, yield strength and elongation of 7A36 alloy extruded tube can reach 696, 655 MPa and 14.0%, respectively, under the optimal heat treatment. Compared with the process of direct chill casting (DC) ingot & extrusion with high extrusion ratio, the size of grain and precipitated phase is smaller, the width of precipitation free zone is narrower under the process of forging ingot & conventional extrusion, which significantly affects the strength.At the same time, the alloy shows high quenching sensitivity. During solution treatment, quenching micro-cracks are easily induced near Fe-rich phase, which significantly affects the elongation of alloy extruded tube.

Keywords

• ultrahigh strength aluminum alloy
• extruded tube
• heat treatment
• microstructure