On the feasibility of AISI 304 stainless steel laser welding with metal powder

An YLS6000 continuous laser was used to weld DP980 to a 1.5 mm thick A6061, and Cu foil with different thickness was pre-placed at the joint prior. According to this, the effect of Cu content on the microstructure transformation and mechanical properties of the microstructure and the mechanical properties of the Fe-Al laser welded joints were discussed, and summed up in two points: On one hand, a higher Cu content was in favor of generating a weld seam with a low δ-ferrite content, and the microhardness increased from 277 HV to 346 HV. On the other hand, Cu stacked on the surface of the Fe-Al intermetallic compounds (IMCs) and suppressed the interdiffusion of Fe and Al, while also replacing Fe to generate (Fe, Cu)2Al5 and (Fe, Cu)Al3, which have excellent mechanical properties. Thus, a higher Cu content was beneficial for decreasing the microhardness and thickness of the IMCs layer and improving the shear tensile strength of the welded joints, which was ~7% higher than that of the directly welded samples.

Effect of Cu content on microstructure transformation and mechanical properties of Fe-Al dissimilar laser welded joints

A laser welding of DP780 steel to Al5052 joint has been investigated to optimize the weld width and lap-shear force. Four types of steel-Al welded joints and fracture model have been proposed. Response surface methodology and central composite design were applied to develop mathematical relationships between the control parameters and the responses. Then, the validation and optimization experiments were carried out to check the models adequacy. The results show that there exists good consistency between the predicted and actual value. This indicates the developed models could predict the weld width and lap-shear force within the limits of the process parameters.

Optimization of laser welding of DP780 to Al5052 joints for weld width and lap-shear force using response surface methodology

In this study, galvanized high-strength steel and aluminum alloy sheets were laser-welded in zero-gap lap joint configuration. In order to determine the influences of the heat input levels, microstructural and mechanical properties of the joints were investigated. The weld bead geometry, microstructure, and intermetallic phases at the interface of welded joints were investigated using an optical microscope and scanning electron microscopy (SEM) with energy-dispersive spectroscopy (EDS) at different heat input levels. Mechanical properties and microhardness distribution of the welded joints were examined according to the weld bead dimension. The results revealed that there is a correlation between the weld seam geometry and intermetallic phase formation. At relatively high heat input level, the penetration depth increased, and thick Al-rich intermetallic layer was observed at the interface of the weld seam, which deteriorated the tensile strength of the joint. It has been found that without the need for any additional precaution, the thickness of the IMC layer can be limited to 5–15 μm when the optimum welding parameters were conducted. The experimental results showed that with limited heat input and penetration depths, up to 108.7-N/mm tensile strength could be achieved and fracture initiated at the weld seam–steel interface.

Investigations on the microstructure and mechanical properties of laser welded dissimilar galvanized steel–aluminum joints

In this paper, we describe experimental laser welding-brazing aluminum alloy to galvanized steel using an external magnetic field. The morphology, microstructure and phase transition at interface was carefully investigated using scanning electron microscope, energy diffraction spectrum and X-Ray Diffractometer. The reaction mechanism of steel/Al welds was also discussed. The results showed that the banded structures with zigzag pattern morphology were produced near the steel matrix. The thickness difference at interface was closely associated with characteristics of laser heat source. The introduction of Zn element in filler metals induces the presence of η-Al5Fe2Zn0.4 phase and δ-FeZn10 phase at the steel interface. These non-brittle phases have good ductility, which can effectively reduce the susceptibility of hot cracking of weld metal and improve the behavior of interface bonding. Meanwhile, fine columnar crystals and eutectic structures formed near the Al matrix as the result of dissolution of Al matrix and regulation of the ampere force. In addition, it has been also found that the metallurgical reaction at interface can be mainly divided into three stages: the solute transfer process, the initiation and the growth of non-brittle phases. The driven effect of magnetic field on molten pool can effectively control the size and distribution of non-brittle phases such as Zn-Al eutectic phases, greatly improving the interfacial performance.

Interface characteristics and reaction mechanism of steel/Al welds produced by magnetic field assisted laser welding-brazing

Welding of steel to aluminum alloy is a difficult work due to the formation of brittle intermetallic compounds. In order to improve the quality of the dissimilar materials weld joints, metal powders are pre-placed on the surface of aluminum alloy prior to welding. In this study, laser welding technique is employed to join DC04 steel to 6016 aluminum alloy with pre-placed metal powders in a lap joint configuration. The morphology, micro-structure and elemental composition of the joints are characterized using SEM equipped with an EDS and optical micro-scope while the micro-hardness and tensile strength are measured. It is indicated that although metal powders do not form compounds directly with Fe or Al, they prevent the contact of Fe and Al. Tensile experiments show that the pre-placed metal powders can significantly improve the joints’ tensile properties. The combined Taguchi-response surface method approach is employed to optimize the laser welding parameters and the optimal condition to have a quality weld is found at laser power 1344.73 W, welding speed 30 mm/s, Defocus distance −2 mm, Shield gas flow 30 L/min. Confirmation experiment proves that the Taguchi-response surface method is an effective way to optimize welding parameters to gain higher mechanical resistance reach to 165.24 N/mm and the bead appearance of optimization joint with fish scales and without cracks.

Zhengwei Ma

Papers

Parameter optimization of laser welding of steel to Al with pre-placed metal powders using the Taguchi-response surface method