Aluminium castings have been widely used in many industries, including automotive, aerospace, telecommunication, construction, consumer products, etc., due to their lightweight, good electric and thermal conductivity, and electromagnetic interference/radio frequency interference (EMI/RFI) shielding properties. The main applications of aluminium castings are in automotive industry. For lighweighting purposes, more and more aluminium castings are used in the automotive vehicle structures to reduce weight, improve fuel efficiency, and reduce greenhouse gas emissions. However, due to the features of cast aluminium, such as porosity, poor surface quality, a tendency toward hot cracking, and low ductility, joining these materials is problematic. In this paper, the joining technologies for aluminium castings and the related issues, mainly cracking and porosity, are reviewed. The current state-of-the-art of joining technologies is summarized, and areas for future research are recommended.

The microstructural evolution following compression and subsequent sub-solvus and super-solvus heat treatment was studied in the Ni-based superalloy, RR1000, typically used for rotor disc applications in aero-engines. For a low strain rate of 0.1 s⁻¹ at close to solvus temperature, 1413 K (1140 °C), the flow stress is constant. For larger strain rates of 1 and 10 s⁻¹ at sub-solvus temperature, 1373 K (1100 °C) dynamic re-crystallization (DRX) of γ grains occurs during forging with accompanying stress decay. Incoherent primary γ′ precipitates form mainly via meta-dynamic re-crystallization (MDRX) at 1 s⁻¹ and are as intergranular. For 10 s⁻¹, the coherently nucleated or existing precipitates present in the initial as-HIP condition become incoherent when the grain boundary sweeps past them during DRX and subsequent grain growth. The incoherent primary γ′ precipitates are mainly intragranular. During sub-solvus heat treatment at 1373 K (1100 °C), dissolution of the incoherent precipitates occurs through coarsening of the coherent intragranular population with only sporadic incoherent precipitates remaining. The prior induced deformation (strain and strain rate) influences the evolution of precipitate morphologies during cooling following heating to super-solvus temperature. Using numerical simulations, a quantitative calculation of the different precipitate morphologies was carried out during slow cooling from super-solvus temperature, 1443 K to 1373 K (1170 °C to 1100 °C).

The influence of Mn segregation that occurs during casting on recrystallization kinetics has been explored for a C-Mn automotive steel. A homogenization heat treatment was used to remove Mn segregation, while maintaining a similar initial austenite grain size to the segregated condition, to provide base-line comparison data. Deformation trials were carried out in a Gleeble thermomechanical simulator to 0.3 strains at 900 °C, and significant differences in both recrystallization times and final grain sizes were seen between the two conditions. The segregated sample incurred a longer recrystallization time and a wider recrystallized grain size distribution than the homogenized sample. A finite element model was used to predict the local deformation strains based on variations in material properties caused by segregation; the model used data from XRF elemental mapping of Mn to define the local mechanical properties based on differences in solid solution strengthening. Local strain variations ranging from 0.19 to 0.49 were predicted in the segregated sample for an overall applied 0.3 strain (compared to 0.26 to 0.35 in the homogenized sample); using these strains to predict the recrystallized grain sizes gave a much better prediction for the grain size distribution.