Aluminium alloys are widely used in many industries due to their high strength-to-weight ratios and resistance to corrosion. Due to their specific thermophysical properties and intricate physical metallurgy, these alloys are challenging to weld. Work-hardened alloys may experience strength loss in heat-affected zones (HAZ). The strength of precipitation-hardened alloys is severely damaged in both HAZ and weld metal due to coarsening or full dissolution. The high thermal conductivity and reflectivity of aluminium causes lower laser beam absorptivity with lower processing efficiency. Weld imperfections such as porosity, humping, and underfills are frequently formed due to the low melting point and density promoting high liquidity with low surface tension. Porosity is the most persistent imperfection and is detrimental for mechanical properties. In this work, extensive review was made on laser beam and laser-arc hybrid welding of aluminium alloys. Solidification cracking, evaporation of alloying elements, porosity and keyhole stability, and other challenges are studied in detail. The current development of laser welding of aluminium alloys is not so mature and new discoveries will be made in the future including the use of newly developed laser systems, welding consumables, welding methods, and approaches.
Abstract High-power lasers are very effective in welding of plates thicker than 10 mm due to the keyhole mode. High-power intensity generates a vapor-filled cavity which provides substantial penetration depth. Due to the narrow and deep weld geometry, there is susceptibility to high hardness and weld defects. Imperfections occur due to keyhole instability. A 16-kW disk laser was used for single-pass welding of 12- to 15-mm thick plates in a butt joint configuration. Root humping was the main imperfection and persisted within a wide range of process parameters. Added arc source to the laser beam process may cause increased root humping and sagging due to accelerated melt flow. Humping was mitigated by balancing certain arc and other process parameters. It was also found that lower welding speeds (< 1.2 m/min) combined with lower laser beam power (< 13 kW) can be more positive for suppression of humping. Machined edges provided more consistent root quality and integrity compared with plasma cut welded specimens. Higher heat input (> 0.80 kJ/mm) welds provided hardness level below 325 HV. The welded joints had good Charpy toughness at − 50 °C (> 50 J) and high tensile strength.
The conventional micromechanical approaches today are still not able to properly predict the ductile-to-brittle transition (DBT) of steels because of their inability to consider the co-operating ductile fracture and cleavage mechanisms in the transition region, and simultaneously to incorporate the inherent complexity of microstructures. In this study, a complete methodology with coupled cellular automata finite element method (CAFE) and multi-barrier microcrack propagation models is presented to advance the prediction of DBT. The methodology contains three key elements: (i) a multiscale CAFE modelling approach to realize the competition between ductile damage and cleavage fracture and embrace the probabilistic nature of microstructures, (ii) a continuum approach to estimate the effective surface energy for a microcrack to penetrate over particle/matrix interface, and (iii) a method to calculate the effective surface energy for the microcrack to propagate across grain boundaries. The prediction of DBT therefore needs only (1) the stress-strain curves tested at different temperatures, (2) the activation energy for DBT, (3) the ratio between the size of cleavage facets and cleavage-initiating defects, and (4) key statistical distributions of the given microstructures. The proposed methodology can accurately reproduce the experimental DBT curve of a low-carbon ultrahigh-strength steel.
In the present investigation, wire arc additive manufacturing of Inconel 625 was carried out with the cold metal transfer variant of the metal inert gas process. The heat input varied between 0.46 and 0.63 kJ/mm, which is a rather low heat input with low deposition rate. The built walls were subjected to Charpy V and crack tip opening displacement (CTOD) fracture toughness testing, in addition to microstructure examination with light microscope and scanning and transmission electron microscope. The results obtained show that hardness increases from the base metal level of 210, via the heat-affected zone (in the building plate) with HV of 220, to the weld metal, with a hardness of around 240–250. All individual Charpy V values fall within the range from 160 to 200 J, while the CTOD fracture toughness is within the range from 0.49 to 1.05 mm. The microstructure examination revealed the microsegregation of certain elements to the interdendritic regions, causing three different particle types to form. Particles with a spherical morphology were identified as spinel (MgAl2O4). Some of the spinel particles were surrounded by disc-shaped precipitates, which were identified as (NbTi)(CN), having the same orientation as the spinel.
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