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Joining of Aluminum and Steel using AlSi12 Brazing Filler in a Protective Atmosphere Furnace: Microstructure and Mechanical Properties

Yijun Man （ Singapore Institute of Manufacturing Technology, 73 Nanyang Drive, Singapore 637662 ）

Dayou Pan （ Singapore Institute of Manufacturing Technology, 73 Nanyang Drive, Singapore 637662 ）

Shibo Liu （ Singapore Institute of Manufacturing Technology, 73 Nanyang Drive, Singapore 637662 ）

https://doi.org/10.37155/2717-526X-0302-2

Abstract

Brazing of pure aluminum (Al) to steel using an Al-12 wt. %Si (AlSi12) filler metal and an Al brazing flux was performed in furnace filled with protective atmosphere. Microstructure characterizations of the full/fractured joints, tensile shear strength and micro-hardness tests were performed on the samples with holding time from 5-30 min at brazing temperature of 600 °C and additional thermal exposure of 30 min at temperature of 480 °C. It is found that the joint seam for all samples features roughly into four layers, among them, the layer adjacent to steel is an IMC layer and dominantly distributed with h phase. The tensile shear strength of joints is inversely proportional to the thickness of h phase layer and particularly governed by a specific zone which is located in the h phase layer, directly adjacent to the interface between h phase layer and steel and scattered with a lot of visible pores and cracks. Micro-hardness tests show the hardness of the h phase layer remains the highest for each holding time and increases with the increase of holding time. The higher hardness leads to the limited plasticity of the η phase and more fragile of this layer. Furthermore, great differences of hardness exist between the η phase layer and steel may also generate great stresses that induce the crack initiation in the specific zone and finally result in the failure of brazed joints.

Keywords

Furnace brazing; Dissimilar material; Pure aluminum; Steel; Al-12 wt. %Si filler metal; Flux; Intermetallic compounds (IMCs); Tensile shear strength; Microstructure; Micro-hardness

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