Sammendrag
During the production of high-strength 7999 aluminum alloys, hot tearing has set up serious
obstacles for attaining a sound billet/slab. In this research, some typical 7999 alloys were
studied using constrained rod casting together with the measurement of thermal contraction and
load development in the freezing range, aiming at investigating their hot tearing susceptibility.
The results showed that the hot tearing susceptibility of an alloy depends not only on the
thermal contraction in freezing range, which can decide the accumulated thermal strain during
solidification, but also on the amount of nonequilibrium eutectics, which can effectively
accommodate the thermally induced deformation. Our investigations reveal that Zn content has
very profound effect on hot tearing susceptibility. The Zn/Mg ratio of the alloys also plays a
remarkable role though it is not as pronounced as Zn content. The effect of Zn/Mg ratio is
mainly associated with the amount of nonequilibrium eutectics. Grain refinement will considerably
reduce the hot tearing susceptibility. However, excessive addition of grain refiner may
promote hot tearing susceptibility of semi-solid alloy due to deteriorated permeability which is
very likely to be caused by the heavy grain refinement and the formation of more intermetallic
phases.
obstacles for attaining a sound billet/slab. In this research, some typical 7999 alloys were
studied using constrained rod casting together with the measurement of thermal contraction and
load development in the freezing range, aiming at investigating their hot tearing susceptibility.
The results showed that the hot tearing susceptibility of an alloy depends not only on the
thermal contraction in freezing range, which can decide the accumulated thermal strain during
solidification, but also on the amount of nonequilibrium eutectics, which can effectively
accommodate the thermally induced deformation. Our investigations reveal that Zn content has
very profound effect on hot tearing susceptibility. The Zn/Mg ratio of the alloys also plays a
remarkable role though it is not as pronounced as Zn content. The effect of Zn/Mg ratio is
mainly associated with the amount of nonequilibrium eutectics. Grain refinement will considerably
reduce the hot tearing susceptibility. However, excessive addition of grain refiner may
promote hot tearing susceptibility of semi-solid alloy due to deteriorated permeability which is
very likely to be caused by the heavy grain refinement and the formation of more intermetallic
phases.