Processo “MIG-Brazing” : variáveis, aplicabilidade e avaliação das propriedades da junta

Abstract

Due to the increased use of galvanized steel sheets in automotive industries, there has been a search in recent years for joining processes that reduce damage to the coating of these materials. In this context, MIG-Brazing process proves to be very interesting, combining high efficiency and low heat input, reducing the burning of galvanized sheet coating compared to conventional arc welding processes. This work evaluates the applicability and the variables of MIG-Brazing process in the joining of uncoated and zinc coated (galvanized sheets) thin steel sheets and evaluates the properties of brazed butt joints from this process. A mechanized brazing procedure was developed using pulsed current and a fixation device designed to ensure better process results. Two different filler metals (BT 531 and BT 513 bronze alloys) were compared on two types of steel sheets (zinc coated and uncoated). Butt-top joints with different gap distances were made to verify the influence of this parameter in brazed joint resistance. The brazed specimens were submitted to visual and metallographic examination and the electrical signals of the process were collected by software (WeldView) for further analysis of the metal transfer mode. Specifically in relation to galvanized sheets, zinc burning caused by GTAW (Gas Tungsten Arc Welding) was compared to that from MIG-Brazing. Scanning electron microscopy (SEM) analyzes were also performed of the fracture regions of the tension test specimens. The obtained results allowed to positively evaluate the applicability of MIG-Brazing process for joining of uncoated and zinc coated thin steel sheets, since the brazed beads had good visual aspects and the joints had good mechanical resistance. The process still showed advantages for joining of galvanized steel sheets over GTAW process, concluding the possibility of a viable methodology for executing mechanized MIG- Brazing for the joining of thin steel sheets.