| Summary: | To confirm the factors of deteriorating the mechanical properties of joints and the law of transformation behavior along welds thickness, different rotation speeds were conducted for friction stir welding Ni50.7Ti49.3 alloy. Results showed that intermetallic compounds were deteriorated the mechanical properties of joints, and the joint failed before the martensitic platform appeared. W13Re7 and Ti2Ni granular shaped were distributed at the shoulder affected zone (SAZ), and this region was embrittled. Removing the brittle layer of welds surface via post-welded pickling (PWP), the tensile strength of joint at a rotation speed of 600 rpm reached 751 MPa, which reached 79.1% compared with that of the base metal (BM). After the friction stir welding (FSW), the DSC was exhibited the martensite–austenite phase transformation (B19′–B2) in the pin affected zone (PAZ) and SAZ, shown shape memory effect. Phase transformation temperatures (TTs) drifted forward to positive direction about 20 K after welding. Transformation hysteresis in SAZ decreased from 19.46 °C to 12.36 °C with increasing rotation speed from 475 rpm to 950 rpm under heat and deformation of FSW process. Keywords: Friction stir welding, Intermetallic compounds, Nitinol, Shape memory alloy, Phase transformations
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