Microstructures and Mechanical Properties of Dissimilar Al/Steel Butt Joints Produced by Autogenous Laser Keyhole Welding

Li Cui,Li Chen,Dingyong He,Wei Qian,Boxu Chen

doi:10.3390/met7110492

Li Cui, Li Chen + Show 3 more

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https://doi.org/10.3390/met7110492

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Abstract

Dissimilar Al/steel butt joints of 6.0 mm thick plates have been achieved using fiber laser keyhole welding autogenously. The cross sections, interface microstructures, hardness and tensile properties of Al/steel butt joints obtained under different travel speeds and laser beam offsets were investigated. The phase morphology and thickness of the intermetallic compound (IMC) layers at the interface were analyzed by scanning electronic microscopes (SEM) using the energy-dispersive spectrometry (EDS) and electron back-scattered diffraction (EBSD) techniques. The results show that travel speeds and laser beam offsets are of considerable importance for the weld shape, morphology and thickness of IMC layers, and ultimate tensile strength (UTS) of Al/steel butt joints. This proves that the IMC layers consist of Fe2Al5 phases and Fe4Al13 phases by EBSD phase mapping. Increasing laser beam offsets from 0.3 mm to 0.7 mm significantly decreases the quantity of Fe4Al13 phases and the thickness of Fe2Al5 layers at the interface. During tensile processing, the Fe2Al5 layer with the weakest bonding strength is the most brittle region at the interface. However, an intergranular fracture that occurred at Fe2Al5 layers leads to a relatively high UTS of Al/steel butt joints.

Highlights

Dissimilar joining of Al/steel joints has become increasingly significant in industrial applications with a particular weight-saving interest [1,2]
The relationship between the intermetallic compound (IMC) layer thickness and the ultimate tensile strength (UTS) of Al/steel joints has been proposed proposed by Borrisutthekul [12], showing that the UTS was increased with decreasing thickness of by Borrisutthekul [12], showing that the UTS was increased with decreasing thickness of the reaction the reaction layer
IMC layer thickness was clearly observed, which is in good agreement with the results reported by was clearly observed, which is in good agreement with the results reported by Borrisutthekul [12]

Summary

Introduction

Dissimilar joining of Al/steel joints has become increasingly significant in industrial applications with a particular weight-saving interest [1,2]. Research on joining dissimilar steel/Al alloy joints with fusion-based welding processes is extensive, most previous studies have been focused on lapped joints or overlap joints of less than 2 mm thick sheets for automotive applications [2,3]. The development of fast-speed vessels requires improved solutions to the dissimilar joining of Al alloy superstructures to the steel hull for achieving weight reduction in the shipbuilding industry [4,5]. The dissimilar joining of thick Al/steel joints has received considerable attention in shipbuilding applications [6]. It is highly important to develop new welding process for dissimilar joining Al/steel joints directly

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