RESISTANCE WELDING OF SHAPE-MEMORY COPPER--ALUMINIUM ALLOY.

Cu--Al based shape-memory alloys (SMA) are an attractive replacement for expensive SMA of Ti--Ni system in fasteners, thermal automatic device activators, and superelastic elements of instrumentation. Therefore, the problem of joining the latter in different combinations with similar material and other structural metals has become urgent. The main requirement to such joints, in addition to strength, is preservation of functional characteristics, namely temperature range of shape restoration at thermoelastic martensite transformation. Weldability of Cu--Al alloys in the form of 0.05 mm thick foil, 0.3 mm thick strip and 1 mm diameter wire by spot and butt capacitor-type welding was studied, and it was shown that at pulsed welding heating the functional characteristics in the welding area are preserved in joints with rupture strength, corresponding to the respective base metal strength. Metallographic examination showed recrystallization of the initial coarse-crystalline metal in welding heating zone with formation of fine-crystalline structure, both in the solid-state joints and around the cast nugget in spot welding of 0.3 mm strip. Sound butt joints of SMA and copper wire were produced. [ABSTRACT FROM AUTHOR]