Machinability of Cu-Al-Mn Shape Memory Alloys

Cu-Al-Mn (CAM) shape memory alloys (SMAs) are cost effective, have a high low-cycle fatigue life and superelastic limit, and a wide temperature application range compared with other types of SMAs. These characteristics of CAM SMAs have resulted in increased interest in their use in civil engineering applications, particularly as reinforcement in concrete structures and as dampers in steel structures. However, these applications require machining of the CAM SMA bars for connection with other structural elements. This study presents the methods and results of the first systematic research on the machinability of CAM SMAs. The key machinability characteristics of CAM SMAs: chip formation, cutting temperature, tool wear, workpiece surface roughness, and diameter deviation, were studied and compared with those of conventional NiTi SMAs and commonly used steels: mild steel (MS) and 304 stainless steel (SS). The effects of a wide range of cutting parameters: cutting speed ranging from 15 to 120 m/min, feed rate ranging from 0.1 to 0.2 mm/revolution, and depth of cut ranging from 0.5 to 1.5 mm, were investigated. The results from this study showed that the tool wear from machining CAM SMAs was close to that from machining SS and slightly higher than that from machining MS, but much lower than that from machining NiTi SMAs. In all the cases considered here, the tool wear from machining CAM SMAs was found to be 0.6-1.8 times that from machining SS, 0.8-2.4 times that from machining MS, and 1/7-1/21 that from machining NiTi SMAs. After a continuous machining test with a total cutting length of 4.5 m, the nose wear from machining CAM SMAs was found to be 1.6 times that from machining MS, the average flank wear from machining CAM SMAs was found to be three times that from machining MS, and the diameter deviation (relative diameter difference from that of the first sample) of CAM SMAs was only 10 mu m larger than that of MS.