Laser Welding Of Magnesium Alloy Research Articles

Vacuum laser beam welding of AZ31 magnesium alloy: Weld formability, microstructure and mechanical properties

Laser welding of magnesium alloy is still challenging because of the frequently occurred defects. In this work, a promising vacuum laser welding technique was used to join AZ31 magnesium alloy. The effect of ambient pressure on weld surface appearances and weld fusion cross sections was symmetrically investigated. It was found that the penetration depth increased and the weld width became narrower with the descending of ambient pressure from 101 kPa to 10 kPa. However, the penetration depth did not increase and even decreased when the ambient pressure further decreased to 1 kPa and 0.1 kPa. In addition, hump defects occurred at lower ambient pressure of 1 kPa and 0.1 kPa. The weld pool and keyhole behaviors were in-site observed using a high-speed camera at various ambient pressures. The results showed that unstable keyhole and turbulent flow were found in the molten pool at 101 kPa. The keyhole became more stable as the ambient pressure decreased from 101 kPa to 10 kPa. When the ambient pressure further decreased to 1 kPa and 0.1 kPa, the liquid metal thickness between keyhole wall and weld pool periphery became very narrow, which sometimes resulted in unstable absorption of the laser energy. Finally, a 10 mm-thick bottom-locking weld was made under vacuum. The average grain diameter of the weld in vacuum is 28.4 μm, which is much lower than 46 μm in atmosphere. The tensile results showed that the average ultimate tensile strength and the elongation of the joints welded in vacuum at 10 kPa was 8.8 % and 44.0 % higher than that of the joints welded in atmosphere respectively. The enhanced mechanical properties were attributed to the reduced porosity and refined microstrustures of the weld joint made under vacuum.

Mechanisms of Cracking in Laser Welding of Magnesium Alloy AZ91D

Considerable research has been carried out to study the laser welding of magnesium alloys. However, the studies are mainly devoted to butt welding, and there has been limited information in the published literature concerning the bead-on-plate laser welding of AZ91D, even though bead-on-plate welding is required for the repair of cast AZ91D parts with surface defects. In the present investigation, surface cracking of the weld metal was observed when an AZ91D magnesium alloy was bead-on-plate welded using the laser welding method. This paper presents the experimental results and analyses to show that the cracking is “solidification cracking” initiated from the weld surface under high thermal stresses. This is in contrast to the “liquation cracking” observed in heat affected zones in tungsten inert gas welding of the same magnesium alloy. Laser power was found to be one of the main factors affecting the distance of the crack propagation. The higher laser power resulted in longer crack propagation distance into the weld metal. It is demonstrated that hot cracking could be avoided by lowering the laser power and welding speed.

A Parametric Study on Laser Welding of Magnesium Alloy AZ31 by a Fiber Laser

Laser welding of wrought magnesium alloy has been investigated through experimentation and simulation. Laser butt welds and laser lap welds were performed on 2.0 mm thick magnesium alloy AZ31 plates using a 1 kW fiber laser and shielded with argon gas. The effects of laser power and welding speed on weld geometry and microstructure were investigated. Tensile tests were performed to verify weld quality. Through experimentation, a novel processing map was created, which gives the ranges of operating parameters of laser power and welding speed that resulted in viable, defect-free welds. Numerical simulations were performed to predict the weld pool geometry and keyhole stability, and resultant microstructures are shown to be in good agreement with experimental results.

Disk Laser Welding of ZE 41 Magnesium Alloy

The paper deals with disk laser welding of magnesium alloy with the content of rare earth elements. ZE 41 magnesium alloy with the thickness of 2.0 mm was used as experimental metal. TruDisk 4002 solid state laser with a wavelength of 1.03 microns and a maximum power of 2.0 kW was used for welding of magnesium alloy. Laser power which was applied ranged from 0.6 to 1.2 kW. The focal position of laser beam was fixed on the surface of magnesium alloy and the welding speed was set to 70 mm/s. Argon with flow rate of 12 l/min was used as shielding gas. Light microscopy, EDX microanalysis and micro hardness measurements across base metal - fusion zone interface were carried out in order to analyze the weld joints.

Study of plasma in laser welding of magnesium alloy

Magnesium-rare earth alloy was welded using the CO2 laser. The surface plasma of laser welding was studied by the spectra and also, the plasma temperature was calculated using the relative intensity of spectral line. The behavior of the plasma was observed with a high-speed camera. The relationship between the welding parameters and plasma temperature was discussed. The results show that laser power has little effect on plasma temperature. With increasing welding speed, plasma temperature decreases first, and then, increases. The cooling effect of the plasma using helium is significant. The plasma recoil is about 7,500 Pa during laser-welded NZ30K because of the lower boiling point of magnesium.

Detection of defects in laser welding of AZ31B magnesium alloy in zero-gap lap joint configuration by a real-time spectroscopic analysis

The effect of surface oxide layer existing at the lap-joint faying surface of magnesium sheets is investigated on the keyhole dynamics of the weld pool and weld bead qualities. It is observed that by removing the oxide layer from the faying surface of the lap joint, a high quality weld can be achieved in the laser welding process. However, the presence of an oxide layer deteriorates the quality of the weld by forming pores at the interface of the two overlapped sheets. The purpose of this paper is to identify the correlation between the integrity of the weld and the interaction between the laser and material. A spectroscopy sensor was applied to detect the spectra emitted from a plasma plume during the laser welding of AZ31B magnesium alloy in a zero-gap lap joint configuration. The electron temperature was calculated by applying a Boltzmann plot method based on the detected spectra, and the correlation between the pore formation and the spectral signals was studied. The laser molten pool and the keyhole condition were monitored in real-time by a high speed charge-coupled device (CCD) camera. A green laser was used as an illumination source in order to detect the influence of the oxide layer on the dynamic behavior of the molten pool. Results revealed that the detected spectrum and weld defects had a meaningful correlation for real-time monitoring of the weld quality during laser welding of magnesium alloys.

Dual-beam laser welding of AZ31B magnesium alloy in zero-gap lap joint configuration

Porosity within laser welds of magnesium alloys is one of the main roadblocks to achieving high quality joints. One of the causes of pore formation is the presence of pre-existing coatings on the surface of magnesium alloy such as oxide or chromate layers. In this study, single-beam and dual-beam laser heat sources are investigated in relation to mitigation of pores resulting from the presence of the as-received oxide layer on the surface of AZ31B-H24 magnesium alloy during the laser welding process. A fiber laser with a power of up to 4 kW is used to weld samples in a zero-gap lap joint configuration. The effect of dual-beam laser welding with different beam energy ratios is studied on the quality of the weld bead. The purpose of this paper is to identify the beam ratio that best mitigates pore formation in the weld bead. The laser molten pool and the keyhole condition, as well as laser-induced plasma plume are monitored in real-time by use of a high speed charge-coupled device (CCD) camera assisted with a green laser as an illumination source. Tensile and microhardness tests were used to measure the mechanical properties of the laser welded samples. Results showed that a dual-beam laser configuration can effectively mitigate pore formation in the weld bead by a preheating-welding mechanism.

Investigations on laser welding of magnesium alloys

AbstractThe welding processes of three different magnesium alloys ZK60, AZ31, and Mg-rare earth alloy NZ30K were studied using a high-power CO2 laser. The microstructure and tensile strength of welded joints were tested and analyzed. With increasing welding speed the tensile strength and total elongation of welded joints of ZK60 alloy are improved. The ultimate tensile strength of the welded joint of ZK60 is 211.18 MPa, 90% of the base metal. The tensile strengths of welded joints of AZ31 and NZ30K are better than those of the base metal. The expansion of the plasma of laser-welded ZK60 is the strongest with the highest temperature.

镁合金激光焊的研究现状及发展趋势

镁合金激光焊的研究现状及发展趋势

Keyhole stability in disc laser welding of AZ31B and AZ61A magnesium alloys and weld metal properties

To confirm the process potential and limitations of laser welding of magnesium alloys, a newly developed disc laser of 16 kW in maximum power was used to weld thin plates of AZ31B and AZ61A alloys. Melting characteristics and weld metal properties were studied under different process parameters. The very high power density of the applied beam caused the keyhole and the molten pool to be unstable. Underfill was the main welding defect limiting the process window and its formation was closely related to the keyhole instability. A process diagram indicating areas of sound and defected welds could be constructed. Sound welded joints could be obtained for AZ31B alloy with similar mechanical properties as that of the base material. The brittle intermetallics network present along the grain boundaries in AZ61A weld metals required a higher energy input to alleviate its detrimental effect on the mechanical properties of the welded joints.

A Comparison of Weld Properties with or without Filler Wire on Laser Welding of Magnesium Alloy for Car Industry

Magnesium alloys are becoming important material for light weight car body, due to their low specific density but high specific strength. However they have a poor weldability, caused by high oxidization tendency and low vapour temperature. In this study, the welding performance of magnesium alloy was investigated for automobile application. The material was rolled magnesium alloy sheet contains 3wt%Al, 1wt%Zn and Mg balance. The effects of filler wire addition was investigated on 2kW Nd:YAG laser welding. For the results, the mechanical properties of welded specimen were similar with base metal in laser welding with and without filler wire. The bridging ability was improved with filler wire without weld properties deterioration on laser welding of magnesium alloy.

Effects of oxide activating flux on laser welding of magnesium alloy

The behaviours of laser welding wrought magnesium AZ31B alloy with oxide activating fluxes (TiO2, SiO2 and Cr2O3) were studied in the present paper. The results showed that the three fluxes all can increase the weld penetration of the laser welding. A larger grain size was exhibited in the weld metal prepared with flux than that in the fusion zone prepared without flux by optical microscopy. Oxide particles were found in the weld metal by electron probe microanalysis (EPMA), when flux was used. The results of tensile tests showed that weld metal without flux has nearly 90% of base metal strength when compared to the ones with flux. The mixed mode fracture was showed in the weld with flux. The main mechanism for the increases in penetration was that the flux coat absorbed more laser energy during the early period of laser action.

Optimization of Nd:YAG Laser Welding of Magnesium

Magnesium alloys have attracted the interest of modern manufacturing industry owing to their higher strength-to-weight ratios and heat conductivity than other alloys. Laser welding will be an important joining technique for magnesium alloys with their increasing applications in aerospace, aircraft, automotive, electronics and other industries. The Nd:YAG laser beam has a reputation for rapid, precise and easy operation in welding of magnesium. In this study the use of an Nd:YAG laser for thin plate magnesium alloy butt welding was optimized. Some important laser processing parameters and their effects on weld quality are discussed. The microstructure and metallurgical defects encountered in laser welding of magnesium alloys, such as porosity, welding cross sections geometry etc. were determined by optic microscopy. The welding parameters (the shielding gas, convey speed of work piece, laser focal position, pulse frequency, and pulse waveform governing the laser beam in thin plate butt welding were evaluated by gometric parameters.

A review of laser welding techniques for magnesium alloys

Laser welding will be an important joining technique for magnesium alloys with their increasing applications in aerospace, aircraft, automotive, electronics and other industries. In this document the research and progress in laser welding of magnesium alloys are critically reviewed from different perspectives. To date, two types of industrial lasers, carbon dioxide (CO 2) and neodymium-doped yttrium aluminum garnet (Nd:YAG), have been used to investigate the weldability of magnesium alloys. Some important laser processing parameters and their effects on weld quality are discussed. The microstructure and metallurgical defects encountered in laser welding of magnesium alloys, such as porosity, cracking, oxide inclusions and loss of alloying elements are described. Mechanical properties of welds such as hardness, tensile and fatigue strength, and other important structural properties are discussed. The aim of the report is to review the recent progress in laser welding of magnesium alloys and to provide a basis for follow-on research.