The influence of quench sensitivity on residual stresses in the aluminium alloys 7010 and 7075

• Published in: Materials characterization Vol. 65; no. Complete; pp. 73 - 85
• Main Authors: Robinson, J.S., Tanner, D.A., Truman, C.E., Paradowska, A.M., Wimpory, R.C.
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Inc 01.03.2012; Elsevier
• Subjects: 7010; 7075; Aluminium alloys; ALUMINIUM BASE ALLOYS; COMPRESSION; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; FORGING; HARDNESS; HEAT TREATMENTS; Incremental deep hole drilling (iDHD); LATTICE PARAMETERS; MATERIALS SCIENCE; MICROSTRUCTURE; NEUTRON DIFFRACTION; Phase diagrams and microstructures developed by solidification and solid-solid phase transformations; Physics; PLASTICITY; PRECIPITATION; Quench sensitivity; QUENCHING; Residual stress; RESIDUAL STRESSES; SENSITIVITY; SOLID SOLUTIONS; Solidification; SOLUTES; SURFACES; TEMPERATURE GRADIENTS; TRANSMISSION ELECTRON MICROSCOPY; Incremental deep hole drilling (iDHD); 7010; Aluminium alloys; Neutron diffraction; Quench sensitivity; Residual stress; 7075; Aluminium base alloys; Machining; iDHD; Incremental deep hole drilling; Residual stresses; Boring; Heat treatments; Quenching; Holes
• ISSN: 1044-5803; 1873-4189
• DOI: 10.1016/j.matchar.2012.01.005

The most critical stage in the heat treatment of high strength aluminium alloys is the rapid cooling necessary to form a supersaturated solid solution. A disadvantage of quenching is that the thermal gradients can be sufficient to cause inhomogeneous plastic deformation which in turn leads to the development of large residual stresses. Two 215mm thick rectilinear forgings have been made from 7000 series alloys with widely different quench sensitivity to determine if solute loss in the form of precipitation during quenching can significantly affect residual stress magnitudes. The forgings were heat treated and immersion quenched using cold water to produce large magnitude residual stresses. The through thickness residual stresses were measured by neutron diffraction and incremental deep hole drilling. The distribution of residual stresses was found to be similar for both alloys varying from highly triaxial and tensile in the interior, to a state of biaxial compression in the surface. The 7010 forging exhibited larger tensile stresses in the interior. The microstructural variation from surface to centre for both forgings was determined using optical and transmission electron microscopy. These observations were used to confirm the origin of the hardness variation measured through the forging thickness. When the microstructural changes were accounted for in the through thickness lattice parameter, the residual stresses in the two forgings were found to be very similar. Solute loss in the 7075 forging appeared to have no significant effect on the residual stress magnitudes when compared to 7010. ► Through thickness residual stress measurements made on large Al alloy forgings. ► Residual stress characterised using neutron diffraction and deep hole drilling. ► Biaxial compressive surface and triaxial subsurface residual stresses. ► Quench sensitivity of 7075 promotes significant microstructural differences to 7010. ► When precipitation is accounted for, residual stress in both forgings are similar.