Effect of Zinc Content and Cutting Tool Coating on the Machinability of the Al-(5–35) Zn Alloys

In this study, Al-5Zn, Al-15Zn, Al-25Zn and Al-35Zn alloys containing 5, 15, 25 and 35 wt% Zn, respectively were produced by permanent mold casting. Their microstructures and mechanical properties were investigated using metallography and universal hardness and tensile tests. Cutting tests of the alloys produced were carried out in a vertical machining center. During the tests, the cutting forces were continuously measured and saved by a software. The roughness of the machined surfaces of the alloy samples was measured accordance with the standard of ISO 4287. It was observed that Al-(5–15)Zn alloys exhibit single phase (aluminum rich α) microstructure while Al-(25–35)Zn alloys exhibit two-phase microstructure consisting of α and zinc rich η. As the zinc content increased the hardness and tensile strength of the alloys increased, but their elongation to fracture decreased. Cutting force, surface roughness, formation of built-up edge (BUE) and built-up layer (BUL), and the size of the chip occurring in the machining of the alloys decreased with increasing zinc content. The machining of the Al-(5-35)Zn alloys with uncoated WC tools results in both lower cutting forces and better surface quality compared to titanium-aluminum-nitride (TiAlN) coated tools. The changes in the cutting properties of the tested alloys with the increasing zinc content were discussed in the based on changes in structural and mechanical properties.