Brazing Behaviour of some 18K Jewellery Gold Alloys with Different Melting Points = Löteigenschaften von 18K-Gold-Schmucklegierungen mit unterschiedlichen Schmelzpunkten

On the concerns in manufacturing jewellery is the optimisation of gold alloys with regard to their brazability. In jewellery the maintaining of mechanical and metallurgical properties and of the carats of the manufactured jewel after brazing and after re-heating operations has to be considered. These problems were investigated studying the behaviour of three kinds of alloys having 18K and different melting points. We focused on a new filler metal (i.e. Au-Ag-Zn-Cu) joining two commercial coloures gold based alloys (i.e. Au-Cu-Ag and Au-Cu-Ag-Pd). Several joints, performed in two different geometrical conditions (i.e. butt and superimposed joints), were produced using an air-propane flame as brazing source. The melting range of each alloy was determined by DTA and the wetting parameters between filler and base alloys by the sessile drop method. The joints were radiographed and characterized by optical and scanning electron microscopy, EDS analyses and microhardness HV 0.1 profile. The investigation highlighted the good wetting behaviour of the filler in respect of the two base materials and a satisfactory brazability as confirmed by the absence of metallurgical discontinuities along the brazed zone. The partially superimposed joints, corresponding to the geometrical configuration mainly used in manufacturing jewellery, proved to be the more siutable brazing working condition.