Tailoring Surface Integrity of Biomedical Mg Alloy AZ31B Using Distinct End Mill Treatment Conditions and Machining Environments

Magnesium alloys are identified as the new generation degradable biomaterials in the biomedical industry. They can prevent secondary operation for the removal of the inserted implant. Nowadays, sustainable manufacturing is promoting the use of low-temperature machining environments over the traditional means. Surface integrity characteristics of the machined surface and tool wear have always been some of the key interests of the researchers. In this research, aluminum titanium nitride-coated cemented carbide end mills were employed in an untreated and cryo-treated condition to machine the biomedical magnesium alloy AZ31B. The experiments were designed using one-factor-at-a-time (OFAT) approach, and milling operations were conducted under three different machining environments, namely wet, cryogenic, and hybrid. Spindle speed, feed rate, and depth of cut were chosen as the input control variables for a comparative study to achieve lowest surface roughness and highest surface microhardness. The results displayed an improvement in the outcome at higher spindle speed (2800 rpm) and lower feed rate (80 mm/rev) and depth of cut (0.5 mm) produced by untreated end mill during cryo-milling. However, the treated end mill performed best with hybrid machining environment (simultaneous application of LN₂ and cutting fluid) during milling. Moreover, in this case, the accumulated oxides were found to form the most uniform and thinnest passivation layer over the milled surface. Higher spindle speed in cryo-milling achieved 27.45 and 19.56% better surface finish than wet and hybrid-milling, respectively. Moreover, higher spindle speed in cryo-milling achieved 14.46 and 8.72% higher surface microhardness than wet and hybrid-milling, respectively. Higher spindle speed in hybrid-milling achieved 14.89 and 6.97% better surface finish than wet and cryo-milling, respectively. Furthermore, higher spindle speed in cryo-milling achieved 7.69 and 4.10% higher surface microhardness than wet and cryo-milling, respectively.