Interplay Between Residual Stresses, Microstructure, Process Variables and Engine Block Casting Integrity

Optimization of the solution heat treatment process to improve mechanical properties of 319 Al alloy engine blocks using the billet casting method

“…However, protective cylinder liners (typically made of gray cast iron) are required to mitigate the insufficient wear resistance of this alloy in the combustion chamber. Thermomechanical mismatch between these dissimilar materials during the heating and cooling associated with casting and heat treatment may lead to the development of large tensile residual stresses following these processes [2,3], which was confirmed in previous studies [3][4][5][6]. If this residual stress exceeds or is near the alloy yield strength (YS), plastic deformation may be induced when the engine block is subjected to service conditions, as observed in a previous study by the current authors, where the maximum distortion occurred in regions of higher residual stress magnitude and lower YS [7].…”

“…Engine block castings, however, contain a wide variation in microstructure throughout the cylinder region due to the complex casting geometry and the application of risers and chills in different locations of the mold [6,23]. In addition, previous studies on heat treatment [11][12][13][14][15][16][17][18][19][20][21][22] utilized water quenching to maximize retention of alloying elements in solid solution.…”

In situneutron diffraction analysis of stress-free d-spacing during solution heat treatment of modified 319 Al alloy engine blocks

“…From these cylinder bridge locations, 363620 mm 'match stick' samples were extracted. Although previous studies found that the cylinder bridge is a high stress region, 4 it was assumed that sectioning to these relatively small dimensions effectively relieved all tensile residual stresses.…”

“…2,3 Relief of tensile residual stress can be achieved with precipitation hardening heat treatments. Previous studies by and Carrera et al, 2 Lombardi et al 4,5 and Wiesner et al 6 determined that solution heat treatment, as well as artificial aging, fully or partially relieved tensile residual stress in aluminium engine blocks. However, proper optimisation of heat treatment parameters with a view to increasing strength and minimising residual stress has not been undertaken, specifically in large engine block castings that have significant microstructural variations throughout the component.…”

The influence of alloy composition on residual stresses in heat treated aluminium alloys

“…The intrinsic strength will be related to strain, strain rate and temperature and the added complication of time dependency at lower temperatures due to precipitation events influenced by microstructure makes accurate modelling and prediction of residual stresses a potentially complicated task [27][28][29].…”