Abstract
A high shear melt conditioning twin roll casting process with thermo-mechanical treatment was tested to increase the tolerance to high impurity levels in recycled aluminium alloy. Applying high shear melt conditioning prior to casting of recycled AA6111 alloy exhibits reduced centre-line segregation and a fine equiaxed grain structure with improved sheet quality. Homogenisation at 540°C for 8 h with annealing at 520°C for 10 min of the melt-conditioned twin roll casting strip (MC-TRC) showed a clear grain recrystallisation, which was better than the conventional twin roll casting TRC strip. The mechanical test showed a significant improvement in the hardness after applying high shear melt conditioning with thermo-mechanical treatment.
Highlights
Because of the increasing demand for weight reduction in the automobile industries, aluminium sheets have great potential to replace heavy metals.[1]
Micrographs of the transverse (TD), longitudinal (RD) and normal (ND) directions from the conventional twin roll casting (TRC) and melt-conditioned twin roll casting strip (MC-TRC) process are shown in Figs. 1, 2 and 3
The results showed less hardness of the as-cast MC-TRC strips with a significant low standard deviation compared with the as-cast conventional TRC strips
Summary
Because of the increasing demand for weight reduction in the automobile industries, aluminium sheets have great potential to replace heavy metals.[1]. In the as-cast microstructure of AA6111, the phase constituents are often Mg2Si, CuAl2, b-Al5FeSi, AlCuMgSi and a-AlFeMnSi.[5] Most of CuAl2, AlCuMgSi and Mg2Si will dissolve and plate-like b-Al5FeSi particles will transform into spherical aAlFeMnSi particles during the homogenisation process.[6] The undissolved coarse particles of the Fe- or Mn-rich phases will deteriorate the thermo-mechanical performance.[7] Rapid solidification is the best method for improving the mechanical properties of recycled aluminium alloy. The twin roll casting TRC process can accomplish rapid solidification and offer an economic process to produce aluminium sheets from recycled aluminium alloy.[8] Traditionally, TRC has been limited to relatively pure aluminium alloys largely because of the tendency for more alloyed materials to stick to the caster rolls and/or develop microstructures with internal and surface defects that are unsuitable for further downstream processing. The most common casting defects in the twin roll cast sheet can be categorised into surface defects or bleeds, internal defects such as centre-line segregation and macroscopic buckling.[9]
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