Effects of cold rolling and heat treatment on the microstructure and hardness of pure aluminium

The present investigation aims to assess the effects of thermomechanical treatments on both the grain refinement and microhardness of aluminium 1145. Aluminium 1145 is commonly utilized in electronic applications owing to its lightweight features and high thermal and electrical conductivities. Despite its low microhardness, which poses a challenge for such applications, its mechanical properties can be improved by means of thermomechanical treatments such as cold rolling and annealing. The experimental procedure involved casting the sample in an open mould, followed by cold rolling at reductions of 50%, 70%, and 80% from the initial 10 mm thickness. Optical microscopy (OM) was employed to investigate the microstructural changes caused by plastic deformation. A greater degree of deformation was observed along the rolling direction with higher reductions, particularly in the 80% cold-rolled sample, where flattened and elongated grains were evident in the normal plane, whereas a lamellar layered structure was observed in the rolling plane. The Vickers microhardness tester was used to measure the microhardness of the cold-rolled samples. The findings revealed that the microhardness increased with greater rolling reductions, with the 80% cold-rolled sample exhibiting a 72% increase compared with the initial 25HV of the as-cast sample. Moreover, recrystallization was identified at 400 °C, and the grain size increased with increasing annealing temperature and duration. At 450 °C, the grains exhibited equiaxed and finer structures with an average size of 95 μm. The trends in microhardness were aligned with recrystallization and grain growth, as they decreased with increasing annealing temperature and time. Notably, at 450 °C, the microhardness reached 25HV, which was equivalent to the as-cast condition.