Brass/Invar bimetal by explosive welding

Thermostatic bimetals (thermobimetals) are materials consisting of layers with different coefficients of thermal expansion. The layer with a higher coefficient of thermal expansion is called active, with a lower—passive. Invar (Ni-Fe alloy) is mainly used as the passive layer and brass (Cu-Zn alloy) as the active layer. Strong adhesion of the layers along the entire length is one of the main requirements for all grades of thermobimetals. In this study, an Invar/brass thermobimetal plate was obtained by explosive welding (EW). The plate was subjected to metallographic, ultrasonic, and mechanical examination. Scanning electron microscope (SEM) showed that the weld interface had the form of uniform waves over its entire surface. Also, melted zones in the crests and troughs of the waves were observed. Energy-dispersive spectroscopy (EDS) line scanning showed that the melted zones consisted of a disordered Cu–Zn–Fe–Ni solid solution (predominately, of Zn and Cu) and undissolved Invar particles. The average microhardness of the melted zones was 350 H_V. A 3-mm-wide strengthened zone along the weld interface was observed. The average tear strength of the Invar/brass weld joint was 550 MPa, which is higher than that of the individual initial metals. The bending testing has shown that the thermobimetal plate is resistant to delamination, which indicates the satisfactory quality of the weld joint. Based on the results obtained from this study, it can be concluded that EW can be used to produce high-quality Invar/brass thermobimetal plates.