Increasing of brazed joint strength of thin sheet metals for arc brazing with different low-melting filler wires

摘要

The future of car body construction foresees an increasing application of high-strength steel grades and multi-material- joints. Joining technologies are facing the challenge of preserving the material characteristics and microstructures of those alloys as well as keeping in mind the formation of intermetallic phases within the joining area. Due to its comparably low heat input, arc brazing with different low-melting filler metals poses a suitable process option for the joining of thin sheet metals. One of the major concerns resulting in the limited industrial application of arc brazing is the formation of a brittle intermetallic phase for multi-material-systems. A second major concern is the effect of under-matching, describing the joining of base materials with lower strength filler metals. For this purpose, arc brazed joints for steel-aluminum hybrid joints with a low-melting zinc-based filler metal as well as arc brazed joints of the high-strength steel, HCT780XD, with copper-based filler metals were investigated within this work. The objective of this work was to analyze the influence of the CMT process as well as of the resulting intermetallic phases on the microstructure and mechanical properties of an overlap joint. For this reason, mechanical tests were conducted as well as metallurgical analyzation. The results showed that it is possible to manage the influence of the intermetallic phase on the resulting mechanical properties with a suitable process control. For the use of the copper-based filler metal for the high-strength steel a positive influence of a defined amount of intermetallic phase in the seam can be obtained. On the other hand, for steel-aluminum hybrid joints the negative influence of the brittle intermetallic phase can be reduced by a managed detachment of the intermetallic phase via a controlled heat input.