Mechanical properties and microstructures of 1100 aluminum subjected to dry machining

Commercial purity 1100 aluminum samples with an initial grain size of 4.6 μm were subjected to dry orthogonal cutting, i.e., without using cutting fluid. The strain distributions in the deformed material ahead of the cutting tool tip were estimated using a metallographic method based on the observation of shear angles. Local flow stress values were estimated using microhardness measurements. Deformation structures developed in the material ahead of the tool tip were investigated at four different locations using transmission electron microscopy (TEM). The microstructure in the primary deformation zone (PDZ) was characterized by elongated subgrains, extending in the direction of the strain gradient. The average thickness of the subgrains was 380 nm and their width was 730 nm. The hardness of the PDZ was 80 kg/mm2, which represented an increase of 80% from the initial hardness. The strains in the machined chips (MC) reached a high value of 2.3. The corresponding microstructure consisted of a mixture of elongated subgrains with dimensions similar to those observed in the PDZ, and recrystallized equiaxed grains with diameters ranging between 25 and 75 nm. This was accompanied with an 8% decrease in the hardness of the MC compared to that of the PDZ. Grain growth occurred in the secondary deformation zone (SDZ) resulting in large equiaxed grains of 1.2 μm in diameter. The use of cooling fluid during machining restricted grain growth in the SDZ by limiting the grain size to 360 nm.