Abstract
Residual stresses (RS), have been studied in extruded 6061Al-15 vol%SiCw composite by neutron diffraction in two different precipitation states, namely T6 and over-annealed treatment (OV) conditions. Quenching from solution treatment prior to ageing to achieve the T6 condition leads to macro-RS, which does not relax during ageing. Additional annealing for the OV condition does lead to total relaxation of the deviatoric term and partial relaxation of the hydrostatic term. Total relaxation of both deviatoric and hydrostatic terms, however, occurs in the unreinforced alloy. Basically, no decrease of the microscopic-RS occurs from T6 to OV condition. Whereas this may be surprising considering the large difference between aluminum matrix yield strength in T6 and in OV; this result is consistent with the small value of the deviatoric RS term in comparison to the yield stress of the alloy in the OV condition.