Study on Charpy Impact Strength of Copper Brazed Butt Joint with BCuP Types Brazing Materials

Abstract

There have been a few reports on the relation to impact strength of copper brazed butt joint with BCuP types brazing materials. However, these results of investigation do not show any definite tendency.
Indifiniteness.of tendency in these experiments was considered to be due to differences in brazing temperature and in joint structure. So, it was tried to obtain a definite impact value under definite brazing temperature.
The results are summarized as follows:
1. With BCuP 2, BCuP 5 brazing materials and brazing temperature at 750°C, 850°C and 950°C, there is a relationship between joint thickness and charpy impact value in a range of temperatures. Charpy impact strength of a definite tendency can be gained with an increasing joint thickness. In a torch brazing where the temperature control is difficult, the relation between joint thickness and impact value differs depending on the joint structure.
2. The relation detwecn brazing temperature and impact value. At brazing temperature of 950°C, impact value was high. It seems that copper base metal was dissolved in molten brazing materials and this was because of an increasing ductile copper phase in the matrix.
For small brazing thickness high impact strength was obtained but when brazing temperature was high and brazing thickness was large, high impact strengh could be gained.
3. Effect of cooling velocity on impact strength at brazing temperature of 850°C degree, structure became acicular dendritic after quenching and in this case, impact strength decreased by about 0.2 Kg.m/cm² at brazing temperature, of 750°C and 950°C, there was not so much difference in the joint structure after quenching.