MICROSTRUCTURES AND PROPERTIES OF PULSED MIG ARC BRAZED–FUSION WELDED JOINT OF Al ALLOY AND GALVANIZED STEEL
QIN Guoliang, SU Yuhu, WANG Shujun
Key Laboratory for Liquid–Solid Structure Evolution and Processing of Materials, Ministry of Education, Shandong University, Jinan 250061
Cite this article:
QIN Guoliang SU Yuhu WANG Shujun. MICROSTRUCTURES AND PROPERTIES OF PULSED MIG ARC BRAZED–FUSION WELDED JOINT OF Al ALLOY AND GALVANIZED STEEL. Acta Metall Sin, 2012, 48(8): 1018-1024.
Abstract Because there are great differences in physicochemical properties and mechanical properties between Al alloy and steel, their joining with high quality and high efficiency is one of difficult problems in study of welding technology. According to their difference in melting point, the brazing–fusion welding technology of Al alloy to steel was developed based on MIG welding. In pulsed MIG arc brazing–fusion welding process, the molten filler metal and Al alloy base metal will form the fusion welded joint, and will form the brazed joint together with unmelted steel plate, which can efficiently prevent the intermetallic compounds (IMCs) from the formation. With the digital pulsed MIG arc welding machine, the brazing–fusion welding of 6013–T4 Al alloy plate to galvanized steel plate was realized with the filler metal of ER4043, and the effect of welding heat input on microstructures and properties of the joint was studied. The results showed that there is a zinc–rich zone in the weld toe of fusion weld in the brazed–fusion welded joint, which is composed of Zn–Al eutectic, Al–rich α solid solutions and Fe3Al. Fe–Al IMCs layer on the brazed interface is 1.05—4.50 μm in thickness and become thicker with the welding heat input being increased. Fe–Al IMCs with sawtooth or tongue shape grow towards the weld, which mainly includes FeAl2, Fe2Al5 and Fe4Al13. With the welding heat input being increased, the tensile strength of the brazed–fusion welded joint firstly increases and then decreases. At the welding heat input of 850 J/cm, the tensile strength of the brazed–fusion welded joint can be up to 229 MPa and the ductile fracture appears in the HAZ of Al alloy. At the lower welding heat input, the brittle fracture easily occurs.
Supported by National Natural Science Foundation of China (No.50905099) and Specialized Research Fund for the Doctoral Program of Higher Education (No.20090131120027)
