Research on Microstructure Characteristics of Welded Joint by Magneto-Optical Imaging Method

Congyi Wang,Yanxi Zhang,Meng Tian,Chuncao Wang,Xiangdong Gao

doi:10.3390/met12020258

Abstract

This paper proposes an approach for analyzing the microstructure evolution of laser welding seam by magneto-optical imaging (MOI). The Faraday magneto-optical effect and magnetic domain theory are used to account for the MOI mechanism. The influence of laser welding on the welded joint was inspected by the analysis of color, grayscale and brightness of magneto-optical images. The relation between the brightness of magneto-optical image and grain size of microstructure is discussed as well, and the characteristics of magneto-optical images of weld microstructure were compared with those of scanning electron microscope (SEM) images. Experimental results show that three regions, including the weld zone (WZ), the heat-affected zone (HAZ), and the base metal (BM) are distributed in the magneto-optical image of the welded joint. The MOI method can investigate the microstructure evolution of welded joints and provide a theory and experimental basis for detecting weld defects.

Highlights

The pixels of row 256 of MO images were shown in Figure 6, which present the variation of MO image on the topside of the weld seam
This paper has proposed a novel approach for researching microstructure of welded joints using MO imaging method under a constant magnetic field
The microstructure of welded joint was studied based on Faraday effect

Summary

Introduction

Laser welding is widely used in manufacturing with a complicated process [1,2,3,4,5,6]. The welded joint microstructures in different areas inevitably make a big differences under diverse welding conditions [7,8,9]. The differences of welded joint microstructures directly decide their properties, such as hardness, toughness, and plasticity [10,11]. The effect of post weld heat treatment on microstructure and fracture toughness of friction welded joint was studied [12]. It is necessary to investigate the characteristics of welded joint microstructure [13]

Objectives

Discussion

Conclusion