Experimental investigation of novel fast–ageing treatments for AA6082 in supersaturated solid solution state

• Published in: Journal of alloys and compounds 2019-11, Vol.810, p.151934, Article 151934
• Main Authors: Zheng, Jing-Hua, Dong, Yangchun, Zheng, Kailun, Dong, Hanshan, Lin, Jianguo, Jiang, Jun, Dean, Trevor A.
• Format: Article
• Language: English
• Subjects: AA6082; Aging (artificial); Automobile industry; Automotive engineering; Automotive parts; Chemical precipitation; Heating rate; High temperature; Mechanical properties; Nucleation; Paint bake; Pre-ageing; Precipitates; Solid solutions; Solution strengthening; Strength; Supersaturated solid solution; Temperature effects; Tensile tests; Yield stress
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2019.151934

Developing a fast-ageing treatment can significantly reduce the current processing time (180 °C × 9 h) of high strength AA6082 automotive components. In this study, a fast ageing treatment in supersaturated solid solution state was developed, such that the mechanical properties can be rapidly achieved after the paint bake (PB) treatment through introducing a pre-ageing (PA) treatment. The determined fast ageing method considered effects of temperature & time, heating rate and subsequent PB on the ageing response. Tensile tests and TEM observations of typical conditions were undertaken to examine evolved strength and precipitate distribution. Results showed that 210 °C was the optimum pre-ageing temperature as uniformly sized and distributed small precipitates were obtained. The final strength of about 280 MPa, that is 95% of the nominal strength for T6 temper, can be obtained within 15 min soaking for fast heating, and nearly this value for slow heating. More prolific nucleation occurred during slow heating, resulting in more finely distributed precipitates and a higher strengthening. It was observed that PB further increased the strength of over-aged alloy pre-aged at a high temperature of 240 °C. The subsequent PB enabled further nucleation of small clusters and growth of the pre-ageing-induced precipitates which were smaller than 20 nm. This resulted in an improvement in the material strength potentially to satisfy the safety requirements in automotive industry. [Display omitted] •Novel fast-ageing treatments of AA6082 in supersaturated solid solute condition have been developed.•Effects of pre-ageing variables, including temperatures and heating rates, on alloy strength, were investigated.•Paint bake increases the strength of pre-aged specimen due to nucleation of clusters and growth of existing precipitates.•Precipitate distributions of fast-aged specimens were characterised using TEM.