Joining of material compounds of aluminium matrix composites (AMC) by arc brazing using Al-Ag-Cu system filler alloy

Abstract

Aluminium matrix composites (AMC) are in the focus of recent research. In the field of lightweight design, dissimilar joints with AMC are of current interest. To ensure the positive properties of AMC—like high specific strength, increased wear resistance, and low coefficient of thermal expansion (CTE)—a suitable joining technique is necessary. This work shows the state of the art of arc brazing using a filler material of the alloying system Al-Ag-Cu. Joints of AMC/stainless steel and AMC/aluminium alloy are investigated. The formation of brittle Al-Fe intermetallic phases in AMC/stainless steel joints must be reduced to obtain a sufficient joint strength. Therefore, an adapted alloying concept is used for the filler material. The filler (40 wt% Al, 40 wt% Ag, and 20 wt% Cu) is alloyed with various contents of Si (1.2, 1.3, and 1.4 wt%). Primarily solidified Si can be seen above 1.3 wt% Si in the microstructure. The melting temperature could be reduced about 10 K by additional Si. The microstructure analyzed by SEM, EDXS, and XRD, as well as the hardness profile of the joining zone, are characterized and discussed. In case of the interface braze metal/aluminium material, the formation of a thin (approx. 5 μm) phase layer, consisting of solid solution of Al, can be seen. Compared with that insights, the phase layer at the interface braze metal/stainless steel consists of intermetallics of the system Fe-Al. The results of the hardness measurements at the interface and XRD patterns prove the presence of Fe₃Al, FeAl, and FeAl₃. Cracks can occur between the brittle phases FeAl and FeAl₃, due to their high hardness of approx. 600 HV0.005 (rep. FeAl) and 1020 HV0.005 (rep. FeAl₃) and in combination of internal stress formation during cooling.