Dendrite Morphology Evolution of Al6Mn Phase in Suction Casting Al–Mn Alloys

The effects of solute element content and cooling rate on the morphology of Al6Mn phase in suction casting Al–Mn alloys were investigated by transmission electron microscope, scanning electron microscope, and X-ray diffractometer. Results show that Al6Mn dendrite morphology with different degrees of development can occur in the microstructure of as-cast Al–Mn alloys. For the Al–4 wt.% Mn alloy, there are small amounts of block Al6Mn crystals at the center of sample, while we see a block Al6Mn phase and a feathery Al6Mn phase in the sample of Al–6 wt.% Mn alloy. Moreover, the block Al6Mn phases in the Al–8 wt.% Mn alloy disappear, and only snowflake-like Al6Mn phases play a dominant role in the microstructure. However, with an increase in Mn content to 10 wt.%, more dendritic trunks are formed, and secondary dendrite arms are degraded more seriously due to the formation of an icosahedral quasicrystal in suction casting. In addition to the effect of Mn content on Al6Mn morphology, with the increase in cooling rate from the center to the edge of samples, the outline diameter of equiaxed dendrite decreases. The evolution of Al6Mn dendrite morphology and the formation of quasicrystal are further discussed.

ANALYSIS OF THE PROPERTIES OF AW2099 ALUMINIUM-LITHIUM ALLOY WELDED BY LASER BEAM WITH AW5087 ALUMINIUM-MAGNESIUM FILLER MATERIAL

EN AW2099 aluminium lithium alloy, 2.0mm in thickness, was used as an experimental material. EN AW2099 belongs to the 3rd generation of aluminium lithium alloys. The third generation was developed to improve the disadvantages of the previous generation, such as anisotropy in mechanical properties, low fracture toughness, corrosion resistance and resistance to fatigue crack growth, as well. Aluminium magnesium 5087 filler wire with a diameter of 1.2mm was used for the welding. Crack free weld joints were produced after an optimization of welding parameters. The microstructure of weld metal and mechanical properties of weld joints were investigated. Equiaxed zone (EQZ) was observed at the fusion boundary. The character of grains changed in the direction towards the weld centre, from the columnar dendrite zone to equiaxed dendrite zone in the weld centre. The microstructure of the weld metal matrix consisted of -aluminium. Alloying elements enrichment was found at the inter-dendritic areas, namely copper and magnesium. The microhardness decrease in the weld metal due to a dissolution of strengthening precipitates was measured. The microhardness was slightly higher in comparison to a weld produced by a laser welding without a filler material. The tensile strength of the weld joint reached around 67% of the base material’s strength and the fracture occurred in the weld metal.

Effects of Laser Beam Parameters on Bendability and Microstructure of Stainless Steel in Three-Dimensional Laser Forming

In this study, the effects of beam diameter and hatch spacing between the scanning paths on the bendability and microstructural behavior of an AISI 316 stainless-steel sheet in three-dimensional laser forming were investigated. The strain on the heating lines and that between the scanning tracks were numerically investigated to elucidate the effects of process parameters. The strain on heating lines and that between scanning tracks were numerically investigated. The increase in hatch spacing caused a larger amount of counter bending to be retained in the unaffected areas between the tracks through a process dominated by a temperature gradient mechanism (TGM), and also caused a lower deformation. The formation of small equiaxed dendrite grains instead of coarse and inhomogeneous austenite grains occurred during the process at a larger beam diameter and smaller hatch spacing, which increased the bendability of the material, owing to the decrease in anisotropy in the microstructure. Moreover, the increase in the grain size of the reheated overlap region of the deformed sample led to a higher bendability. Under these conditions, the microhardness was also increased owing to the grain boundary strengthening effect.

Reliability and sustainability of wire arc additive manufactured plates using ER 347 wire-mechanical and metallurgical perspectives

The steel wall measuring 120 mm in length and 210 mm in height was manufactured by wire and arc additive manufacturing (WAAM) using ER347 wire and gas metal arc welding (GMAW). The mechanical integrity and microstructure of the WAAM treated plate were examined. It was found that the steel plate was well formed, no clear boundaries between the layers were observed, and different thermal history leads to a variety of microstructures. The hardness of the WAAM-processed plate gradually varied from top to bottom and was between 203.5 HV and 248.2 HV. Microstructure of WAAM 347 consists of columnar dendrites and equiaxed dendrite in the multilayer deposition. The percent volume fraction of delta ferrite in the as-deposited WAAM plate was 4.2 and the predicted ferrite number from WRC-1992 diagram is 4.1. The mechanical properties of the welded parts were anisotropic; the sample at 45° orientation has a higher tensile strength compared to 0° and 90° orientation samples. The fractured tensile specimens in the as-deposited state were characterized by dimple-like structures revealing the ductile fracture. SEM line mapping confirms the presence of intermetallic compounds (NbC) in the WAAM 347 plate.

Corrosion Resistance of 2060 Aluminum–Lithium Alloy LBW Welds Filled with Al-5.6Cu Wire

Alloy sheets of type 2060 aluminum–lithium were welded by laser beam welding (LBW) filled with ER2319 Al-5.6Cu wire. Microstructural observations showed the uneven distribution of columnar grains, equiaxed grains and equiaxed dendrite grains in the weld. The θ′(Al2Cu) phase and other phases precipitated in the weld. The θ′(Al2Cu) phase centrally distributed at the grain boundaries. During the immersion corrosion, the pitting corrosion first occurred and then gradually expanded and transformed to intergranular corrosion and exfoliation corrosion. The electrochemical corrosion test showed a higher corrosion tendency of the base metal and heat-affected zone for the lower corrosion potential, but the corrosion current density of the weld was relatively larger. The segregation of Cu, Mg and other elements at the grain boundary aggravated the occurrence of intergranular corrosion.

Growth of Equiaxed Dendrite in Al-20wt.%Cu Alloy by Synchrotron X-Ray Radiography

Synchrotron X-ray radiography was used to in-situ study the growth of equiaxed dendrite during the solidification of Al-20 wt.% Cu alloy. Equiaxed dendrites with two different morphologies were formed in nearly isothermal conditions. The image processing was used to improve the image quality. The time evolution of the primary dendrite arm length and the corresponding growth rates were analyzed. The experimental results indicated that the solute interaction was the main factor to influence the equiaxed dendrites growth. Besides, the rotation and floating of the dendrites were also observed during the early growth phase.

Phase Field Simulation of Solidified Multiple Grains

A phase-field model based on the Ginzburg-Landan theory and KKS model is used to simulate the dendrite growth of multiple grains for Al-Cu alloy. The influence of solidification latent heat and undercooling on the growth of equiaxed dendrite, solute distribution and temperature distribution were studied. The results show that the dendrite has well-developed and the competitive growth between grains more intense with the increasing of undercooling. The release of solidification latent heat restrain dendrite growth to a certain extent, which led to the less developed growth of dendrite solidified in non-isothermal conditions than that in isothermal conditions.