# Cutting Speed and Feed Influence on Surface Microhardness of Dry-Turned UNS A97075-T6 Alloy
## 1 Introduction
Although there are numerous works in the literature that analyzed the influence of cutting parameters on surface microhardness [24; 25; 26], these studies should be completed in the case of dry machining of aluminum alloys. Thus, [PERSON] et al. [27] analyzed the feed and cutting speed influence on the cutting forces and the surface roughness of the UNS A96063 alloy, in dry-turning operations, in order to obtain the optimal machining conditions for low surface roughness (\(Ra\)) and high surface microhardness (\(HV\)). Cutting speed values between 10 and 50 m/min and feed values between 0.40 and 0.80 mm/r were used. A lower roughness and higher microhardness were obtained for intermediate feed (0.5 mm/r) and high cutting speed values (40 m/min). In addition, a potential model was developed in this work. That model allowed obtaining the microhardness as a function of the feed rate, the cutting speed, the cutting forces, and the number of machining steps (roughing and finishing). [PERSON] et al. [28] analyzed the cutting speed and cutting depth influence on the microhardness of dry-turned UNS A97075 alloy. Different cutting speed (50, 100, 200 and 300 m/min) and cutting depth values (0.3, 0.6 and 0.9 mm) were used, whereas the feed remained constant (0.05 mm/r). In this case, a surface microhardness decrease was observed when the cutting speed was increased. In addition, a reduction in the microhardness was also observed when the cutting depth was increased, but its influence was less noticeable. The authors attributed this behavior to the heat generation and dissipation on the machined surface. As previously mentioned, the machining operation modifies the surface microstructure of the machined parts. In this regard, [PERSON] et al. [29] used microhardness measurements to evaluate the depth reached by these microstructural alterations, in the dry turning of UNS A97075-T651 alloy. Several hardness tests were carried out for different surface layer depths (up to 500 \(\upmu\)m). A microhardness reduction was observed as a function of the depth, and it was finally stabilized at greater depths. The cutting speed and the tool-tip radius influence was also analyzed. The results obtained showed that higher cutting speed values resulted in greater microstructure modifications, with a reduction in the grain size. In addition, cutting tools with higher tool-tip radius generated a greater reduction in the grain size and higher values of surface microhardness, as a consequence of the contact surface reduction between the tool and the machined part. Similarly, [PERSON] et al. studied the microstructure modifications as a function of the surface microhardness, in the dry turning of UNS A97075-T651 alloy [30]. In this case, the turning operations were carried out with a constant feed (0.076 mm/r) and cutting speed values between 360 and 720 m/min, while also varying the tool rake angle (0\({}^{\circ}\)-15\({}^{\circ}\)). The authors indicated that the cutting speed increments and low tool rake angle generated a microstructure modification at higher surface depths, as a consequence of the temperature increment in the cutting area. Contrary to the results obtained by [PERSON] et al. in [29], [PERSON] [30] stated that the microhardness in a closer area to the surface decreased until 50-\(\upmu\)m depth. Once this value was reached, the microhardness tended to stabilize at higher values than the initial ones and, therefore, a more homogeneous microstructure was obtained. With regard to the UNS A96061 alloy, [PERSON] et al. [26] performed different conventional and non-conventional machining tests, in order to study the microhardness alterations induced by the process in the part surface. It was observed that, in all tested machining processes, the microhardness decreased in the most superficial layer of the machined part, compared to the starting material. This microhardness reduction is justified by the thermal effect of the machining operation on the machined surface.