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Effect of extrusion temperature on the surface roughness of solid state recycled aluminum alloy 6061 chips during turning operation

Nowadays solid state recycling of aluminum chips provides a competitive market for the aluminum foundry. Chip recycling requires an efficient pretreatment system in terms of optimizing consolidating technique to achieve a high metal recovery with rapid return of investment and hence drive down fixed cost and increase productivity without compromising on metal quality. Solid state recycling through hot extrusion is a promising technique to recycle machining chips without re-melting. In this article, aluminum chips were cold compacted followed by hot extrusion under extrusion ratio of 5.2 and at three different extrusion temperatures of 350°C, 425°C, and 500°C. The effect of extrusion temperature on the surface roughness (Ra and Rz) and machining time needed to remove a unit volume of aluminum alloy 6061 machined by turning were investigated. The effect of extrusion temperature was investigated using the Box–Behnken design; three machining parameters (depth of cut, feed rate, and cutting speed) on the surface roughness of the machined specimens were also examined. Obtained results were in favor of the presence of significant effect of those four parameters on specimen surface roughness with dominating effect of feed rate. Moreover, the optimum cutting conditions for minimum machining time per unit volume (Tm) while Ra is kept below an industrially accepted value of 0.8 μm was found for the original alloy for the following cutting conditions: cutting speed of 116 m/min, depth of cut of 0.33 mm, and feed rate of 0.11 mm/rev.