Multi-Technique Residual Stress Measurements to Quantify Stress Relief of 7085-T7452 Aluminum Die Forgings

Abstract

Abstract This article describes the use of complementary residual stress measurements to quantify cold-work stress relief in die forgings used for monolithic unitized aerospace components. Two specimens were used, being nominally identical, but measured at different processing stages: one that was die forged and quenched (high residual stress state) and one having a post-quench, cold-work stress relief (low residual stress state). Multi-component residual stress maps were developed using multiple techniques along a single measurement plane (axes of this plane run parallel to the nominal long-transverse [x-direction] and short-transverse directions [y-direction]). The measurement techniques were energy dispersive X-ray diffraction (EDXRD), neutron diffraction (ND), and primary slice removal (PSR) biaxial mapping. Good agreement was found between the EDXRD and PSR biaxial mapping measurements. In the high-stress specimen, measured stress normal to the measurement plane (z-direction [L]) is highly compressive along the part exterior (−300 MPa) and highly tensile toward the center (250 MPa), as typical of quenched aluminum. Stress along the x-direction has a similar spatial distribution but smaller magnitude (−200 MPa to 130 MPa). The measured stresses in the cold-worked, low-stress specimen are significantly lower, with z-direction and x-direction stresses ranging between −130 MPa and 75 MPa.