Aluminum-copper (Al-Cu) alloy B206 is a high strength and ductile alloy showing promise for use in automotive suspension components. Incorporation of lightweight B206 alloy in automotive suspension components may significantly reduce overall vehicle weight and increase the vehicle’s fuel efficiency. However, one of the major factors inhibiting the use of B206 is its high susceptibility to hot tearing during casting. Hot tearing is a complex phenomenon attributed to alloy solidification, microstructure and stress/strain development within a casting. Numerous methods (e.g. preheating of mold, grain refinement, elimination of sharp corners in a component) help to reduce the occurrence of hot tears in castings, but the underlying mechanisms responsible for hot tearing remain ambiguous. This research aims to advance the understanding of the mechanisms responsible for hot tearing in B206 Al alloy.
In this research, the conditions associated with the formation of hot tears in B206 were investigated via ex situ and in situ methods. Titanium was added in three levels (i.e. unrefined, 0.02 and 0.05 wt%) to investigate the effect of grain refinement on hot tearing. Ex situ neutron diffraction strain mapping was carried out on the three B206 castings to determine casting strain and stress. Further, in situ techniques were used to establish the onset temperature and solid
fraction of hot tearing in B206 and to improve the understanding of microstructure development in B206.
The results indicate that titanium additions had a significant impact on the hot tearing susceptibility of B206, by effectively reducing grain size and transforming grain morphology from coarse dendrites to fine globular grains. Further, thermal analysis suggested that grain refinement delayed the onset of dendrite coherency in B206 and therefore enhanced the duration of bulk liquid metal feeding for the refined casting conditions. As a result, the interactive effects of such factors resulted in a more uniform distribution of strain, and subsequent higher resistance to hot tearing for the grain refined castings. Finally, in situ analysis determined the onset solid fraction of hot tearing in B206 and provided an understanding of the role of microstructure on hot tearing in B206.