The effect of Al2O3 Nano-particles coated with manganese oxide on the microstructure and mechanical properties of low carbon steel using GMAW process

This paper reports an investigation carried out to determine the effect of aluminum oxide Nano-particles coated with manganese on the microstructure and mechanical properties of single-pass butt joint of low carbon steel plates of 6.0 mm thicknesses using gas metal arc welding process. After selecting appropriate welding parameters and adding 0.25 gr and 0.5 gr of Nano-particles into the joint line and carrying out the welding, the samples were prepared for micro hardness and tensile tests. Furthermore, the sample with optimum Nano-particles having the highest ultimate tensile strength and without having any visible and metallurgical defects in the microstructure was selected for further investigation.  Subsequently, microstructures of the weld without and with optimum Nano-particles were studied using optical microscopy and scanning electron microscopy (SEM) and the fractured surface of the weld obtained from tensile testing was investigated for the samples without Nano particles and the optimum sample with Nano materials were studied. The results show that Nano-particles added to the weld pool penetrated into the weld zone and helped in formation of acicular ferrite in the microstructure. Based on the results obtained, ultimate tensile strength and percentage of elongation of samples without Nano-particles and with optimum Nano-particles were increased from 387 MPa and 6.8% to 408 MPa and 13.6%, respectively. In addition, the average hardness of the weld metal without Nano-particles and with optimum Nano-particles were increased from 158 VHN to 172 VHN respectively