Study of peak temperatures in friction stir spot welding of AA2024-Al/polycarbonate and AA2024-Al/polypropylene systems

Compared to ordinary fusion welding processes, friction stir spot welding (FSSW) have significant advantages for example: joining of conventionally non-weldable alloys, improved mechanical properties and reduced distortion of weldable alloys joints due to the pure solid-state joining of metals. This welding technique gives the online feedback control and opportunity of automation, allowing automatic adaptation to geometrical and environmental variations of the component. However, several fundamentals of the process such as the temperature inside the stirred zone of the weld and its power on mechanical properties, are not yet fully understood. In the present study, FSSW was adopted to weld AA2024 aluminium alloy sheets with both polycarbonate (PC) and polypropylene sheets using two different tools having two different pin configurations. The two tools have conical pin with 2.5 mm height, however, tool (T1) has draft angle of  16.69o and the tool (T2) has a draft angle of  6o.The effects of FSSW parameters of the process, typically, the tool rotational speeds and dwell time, on temperature variation in the tool/work piece interface was also recorded, via an infrared camera. The results revealed that, increasing the tool rotational speed and/or the dwell time increase(s) the peak temperature in FSSW of both AA2024Al/polycarbonate and AA2024Al/polypropylene welded joints. For AA2024Al/polycarbonate joints, the peak temperatures recorded for tool T1 are higher than those recorded using tool T2. The peak temperature ranges were found to vary from 54 to 150 °C and from 45 to 136 °C, for joints welded using T1 and T2 tools, respectively. While, for AA2024Al/polypropylene joints, the peak temperatures recorded for tool T2 are higher than those recorded using tool T1. The peak temperature ranges were found to vary from 40 to 115 °C and from 61 to 143 °C, for joints welded using T1 and T2 tools, respectively.