Impact of pre-ageing on age hardening response of twin-belt cast AlMg1SiCu sheet

The potential of twin-belt cast (TBC) AlMg1SiCu sheet for structural automotive applications was investigated with a particular emphasis on the impact of pre-ageing on its age hardening response. The optimum T6 process for the TBC AlMg1SiCu sheet is identified to be a water-quench from the solution heat treatment at 540 degrees C and a subsequent ageing treatment at 180 degrees C. This process gives hardness values as high as 120 HV within several hours when ageing at 180 degrees C is performed shortly after the solution treatment. The age hardening capacity is impaired, however, when the sheet is stored at room temperature before the artificial ageing cycle. Pre-ageing at 100 and 140 degrees C is effective in improving the age hardening response of the naturally aged 6061 sheet. Pre-ageing suppresses natural ageing and clustering activities and gives lower T4 yet a much higher T6 hardness.