The influence of metallostatic pressure, grain refiner, and modification on the critical solid fraction (CSF) of cast A380 alloy

In this work, porosity formation with regard to the change in the metallostatic pressure was investigated. Different geometry was generated to simulate the effect of pressure on critical solid fraction. A380 alloy was sand cast. Additionally, the effect of grain refiner and modifiers was also investigated. Samples were subjected to X-ray radiography and density measurement to quantify the pore size and distribution.

Evolution of Residual Stress Through The Processing Stages in Manufacturing of Bore-Chilled Sand-Cast Aluminum Engine Blocks With Pressed-In Iron Liners

The cumulative global emissions produced by the automotive industry over the last decade has put a tremendous strain on the environment. Consequently, automotive engineers and manufacturers have been forced to improve the efficiencies of their automobiles which is frequently accomplished by increasing the operating pressure, and therefore temperature, of the combustion engine. Unfortunately, in addition to the rise in operational pressures and temperatures, large tensile residual stresses often accumulate in the cylinder bridges during the casting process of aluminum engine blocks due to the use of cast-in iron cylinder liners, leading to combined stress magnitudes above the strength of the currently used aluminum alloys. Thus, the present study aims to characterize the evolution of residual stress, with application of neutron diffraction, at several critical stages of the manufacturing process of sand-cast aluminum engine blocks that have eliminated the iron cylinder liners from the casting process and replaced them with cylinder bore chills that are pressed-out after the thermal sand reclamation process. The replacement of the iron liners shifted the stress mode from purely tension to purely compression until the bore chills were removed. Following removal of the bore chills, the maximum tensile stress at the top of the cylinder bridge was ~70% lower than the engine’s predecessor which was produced with iron liners. Moreover, in the production-ready state (i.e., T7 heat treated, machined and press-fit liners inserted), the stress mode maintains the partially compressive nature with low magnitudes of tension, thereby lowering the material’s susceptibility to crack growth and propagation.

Microstructural Evolution of Large Cast Haynes 282 at Elevated Temperature

Haynes 282 has attracted attention for casting applications in AUSC power plants due to its good creep properties. However, the market is primarily comprised of wrought Haynes 282, while the cast version is not commercially available. In this study, the microstructure of a large traditional sand cast Haynes 282 was studied from as-cast condition to long-term heat-treated condition by combining experimental data and thermodynamic calculations. The microstructure of a large cast Haynes 282 includes γ, γ’, two types of MX, M23C6 and µ phases. After standard post heat treatment, µ phases were dissolved and precipitated as M6C. The equilibrium state was achieved after 266 h aging at 788 °C, after which γ’ particles began coarsening. These kept to a spherical morphology; the smallest misfit was found with the γ matrix. Once post heat treatment was finished, MX exhibited little morphology and compositional change during the long-term isothermal aging. Grain boundary is covered by discrete M23C6 and M6C precipitates and this morphology keeps stable during isothermal aging. No presence of the needle µ phase have been found at grain boundaries after 10,000 h aging at 788 °C. All these microstructural features indicated that cast Haynes 282 could have a high thermal stability and good creep properties.