Surface integrity study of high-speed drilling of Al–Si alloy using HSS drill

Abstract

The motivation to replace steel and cast iron with Al–Si alloys for automotive components is part of the attempt to improve fuel economy and reduce emissions. In relation to that, the application of high-speed drilling is considered one of the most-used operations in hole making for automotive parts due to its ability to reduce lead time without sacrificing the hole quality. However, this advantage was offset by the creeping problems encountered during high-speed drilling. Although this issue is addressed accordingly, problems like uncontrollable surface integrity and poor hole quality still exist. Surface integrity studies involved the investigation of surface roughness, metallurgical changes and microhardness of the subsurface of the drilled hole. Significant alternations with respect to the loss of mechanical properties have been observed from the microhardness and microstructure analysis of the drilled hole. Results from this study showed that, in general, drilling parameters have significant effects on the surface quality and integrity of the drilled hole during high-speed drilling of Al–Si using an HSS drill.

Machinability properties of Al–7Si, Al–7Si–4Zn and Al–7Si–4Zn–3Cu alloys

“…In addition, silicon particles caused the formation of cavities on the machined surface and reduced surface quality due to the movement of the cutting tool, friction and abrasive effect. This was observed by Farid et al [24] in the machining of Al-Si (Al 383) alloy with HSS drills, whereas it was stated in machining of Mg-added Al-Si alloys by Pramila et al [49]. It was observed that no significant continuous layer was formed under the hole cutting subsurface in the drilling of the Al-7Si-4Zn-3Cu alloy compared to the binary and ternary alloys (Fig.…”

“…Generally, the subsurface microhardness in the region closest to the machined surface of the workpiece reaches higher values. This value decreases with increasing depth of machined surface until it reaches the actual hardness value of the material [24] (Fig. 12).…”

“…In addition, these hard particles also cause wear on the cutting tool during the cutting process. These factors bring about an increase cutting force and surface roughness [24]. In addition, elongation to fracture value of Al-7Si alloy (9.7%) is higher than other alloys, indicating that it is more ductile material.…”

“…This welded structure changes the tool geometry and causes tool wear and reduced surface quality [23]. During the machining of Al-Si alloys, high amount of hard Si particles causes tool wear and increases surface roughness [24]. Some studies on the subject have been conducted in the literature.…”

“…Braga et al [25] found that BUE occurs when drilling the Al-Si alloy with MQL (Minimum quantity lubricant) and diamond coated drill in high feed, and generally the uncoated K10 drill performs better than the diamond-coated drill. Farid et al [24] found that in drilling at high speeds with HSS drills of Al-Si alloy with Al 2 Cu intermetallic phase with increasing machining time and cutting speed, surface roughness is reduced, compression stress on primary silicon particles and plastic flow formation are caused by the distribution and fragmentation during cutting, and compression of silicon particles under the machined hole surface significantly changed the microhardness values. Froehlich et al [26] found that the Al 2 Cu phase acts as a chip breaker in the drilling of AA2217 alloy, contributing to the reduction of adhesion wear, axial force and shear moment of the cutting tool, Edwards et al [27] found that the presence of copper in Al-Si alloys constitutes the Al 2 Cu phase and that the refined and disperse phase facilitates machinability by reducing the plasticity of the material, and Marani et al [28] stated that the machinability of these alloys can be improved by reducing BUE formation in tool rake face during machining with different element additions to Al-Si alloys.…”