Effects of copper addition on intergranular fracture of an Al-Zn-Mg alloy

• Published in: Journal of Japan Institute of Light Metals Vol. 37; no. 5; pp. 375 - 380
• Main Authors: KANNO, Motohiro, SAITOH, Hiroshi, SUZUKI, Hisashi
• Format: Journal Article
• Language: English; Japanese
• Published: The Japan Institute of Light Metals 1987
• Subjects: Al-Zn-Mg alloy; copper addition; grain boundary precipitate; improved ductility; intergranular fracture
• ISSN: 0451-5994; 1880-8018
• DOI: 10.2464/jilm.37.375

The morphology of tensile fracture of Al-6 wt%Zn-1.9 wt%Mg-(03 wt%) Cu alloys subjected to isothermal aging at 125°C were investigated in relation to their tensile properties, precipitate and deformed structures. After prolonged aging, copper-bearing alloys exhibited higher strength and higher elongation compared with the ternary alloy. The improved ductility of copper-bearing alloys was due to the suppression of intergranular fracture. Localized intragranular deformation and preferred deformation within PFZ were similarly observed even in copper-bearing alloys. Intergranular fracture surfaces were commonly composed of numerous dimples which were probably formed by the decohesion of the interface between grain boundary precipitates and the matrix. Copper addition little varied the width of PFZ but markedly refined grain boundary precipitates. The refinement of grain boundary precipitates was considered to be responsible for the suppression of intergranular fracture.