TIG WELDING OF Al 7005/Al2O3 METAL MATRIX COMPOSITES

摘要

The present paper describes the results of welding tests performed on Al 7005/Al_2O_3 alloy composite reinforced with 10 vol. percent alumina particles. TIG welds were produced by joining extruded plates having a thickness of 6 mm and tubes having an outside diameter of 33 mm and a wall thickness of 1,5 mm. Different joint configurations were considered, as shown in figure 2 in the paper. The weld investigated, further differed for the selection of the filler metal. Three different filler wire compositions were chosen with the aim of increasing molten metal flow during welding (Al-5 percent Si / 4043 alloy and Al-12 percent Si/4047 alloy) and of improving the resulting joint strength (Al-5 percent Mg /5356 alloy). In addition, composite filler wires were prepared by longitudinally cutting thin stripes from the Al 7005/Al_2O_3 composite tubes.Microstructural analyses were carried out by optical and scanning electron microscopy to characterise the weld metal and heat affected zone structures of the joints. Mechanical properties were evaluated by microhardness profile measurements and by room temperature tensile tests on cross-weld specimens.The results showed that when using unreinforced filler metals, particle pick up from the parent metal generated a weld metal structure of composite type. The particle distribution featured a slight tendency toward clustering but the maximum local volume fraction achieved was always lower than that of the base metal. No particular welding defect was detected and satisfactory mechanical properties were measured also due to the increase in strength brought about by natural aging effect in the HAZ after welding. The welds performed by using composite filler wires featured promising matrix microstructure and a homogeneous particle distribution. The ability to recover the original T6 temper strength owing to post weld aging of both the heat affected zone and the weld metal was also verified. The use of a composite filler metal also introduced welding defects such as entrapped gas and oxide films that partially impaired the mechanical strength achieved by the joints. It was therefore supposed that improved properties could readily be achieved by a better control of the composite filler metal wire quality.