Reducing residual stresses for optimal machining of Al-6061 (T-6) alloy through re-heating technique

The quenching of aluminum alloy ensures good mechanical properties, however, thermal gradients can be large enough to produce high levels of residual stresses. Upon machining of aluminum alloys, these stresses are released in the form of unwanted deformations making the part unacceptable for use. Re-heating is useful to reduce or eliminate the stresses hence avoiding rejections and reworks during machining. The ¬re-heating cycle for Al 6061-T6 alloy has a soaking temperature of 343 ˚C which in addition to stress reduction also drains out the mechanical properties of the alloy which subsequently reduces the functionality. This paper evaluates the effectiveness of low temperature re-heating for reduction of stresses without affecting the mechanical properties of the alloy. Different re-heating temperatures are employed and mechanical tests are performed on the alloy to identify the post treatment strength and the subsequent reduction in the machining distortion. Re-heating above 300 ˚C reduces the material strength by more than 50% with a simultaneous increase in ductility. The experimental results indicated 60% reduction in distortion with 21 % decrease in the strength.