A review on selective laser sintering/melting (SLS/SLM) of aluminium alloy powders: Processing, microstructure, and properties

Particle-reinforced metal matrix nanocomposites fabricated by selective laser melting : a state of the art review

The automotive industry is facing demands simultaneously to increase its fleet average fuel economy and to reduce the emission of greenhouse gases by its products. In order to meet these new standards, the industry is increasingly aiming to decrease the weight of vehicles through the use of new materials, especially lightweight aluminium alloys. Laser welding is a critical enabling technology in reducing the weight of the body structure through increased use of aluminium and tailor welded blanks. In this review the available research on the laser welding of 5xxx, 6xxx, and some 2xxx series automotive aluminium alloys is critically examined and interpreted from different perspectives. First, the current understanding of the important physical processes occurring during laser welding of these alloys such as energy absorption, fluid flow and heat transfer in the weld pool, and alloying element vaporisation are examined. Second, the structure and properties of these weldments are critically evaluated....

Current issues and problems in laser welding of automotive aluminium alloys

Porosity formation is greatly influenced in aluminium alloys by the low vaporisation point element (Mg, Zn) content, or by process instability such as key-hole closures that tend to entrap occluded gases during welding. Another important contribution comes from the hydrogen content, because of a very high solubility in molten aluminium that favours microporosity generation. In this paper, cw YAG laser welds on two aluminium alloys were carried out: a AA5083-O wrought alloy with a high Mg content (4.5%) and a A356 cast alloy with 7% Si and a cast oxide layer. The porosity content in laser beads was extensively studied, with the use of different experimental method (X-ray radiography+image analysis, tomography), in order to check the influence of mechanical surface preparation as well as process parameters (single or dual spot, different welding speeds). It was concluded that surface preparation as well as dual beam welding are adequate methods for reducing porosity formation tendency in laser assemblies.

Reduction of porosity content generated during Nd:YAG laser welding of A356 and AA5083 aluminium alloys

The proper orthogonal decomposition theorem (Loeve (1955)) of probability theory has been proposed and adapted by Lumley (1967) for detecting spatial coherent patterns in turbulent flows. More specifically, the decomposition extracts deterministic functions from second order statistics of a random field and converges optimally fast in the quadratic mean (I.E. in energy). Aubry et al. (1990) showed that the technique can be made completely deterministic in the sense that it can be applied to (deterministic) spatially and temporally evolving flows. The remarkable property of this deterministic decomposition is not only in its optimal convergence (as emphasized previously in the literature) but also in its space/time symmetry which permits access to the spatio-temporal dynamics. We discuss here the implications of this property for fluid mechanics studies. The flow is decomposed into both spatial and temporalorthogonal modes which are coupled: each space component is associated with a time component partner. The latter is the time evolution of the former and the former is the spatial configuration of the latter. This generalizes the notion of spatial structures to that of temporal structures both of which can be followed through the various instabilities that the flow undergoes as the Reynolds number increases (in the first flow instability stages as well as in the fully developed turbulence). It also provides a nonlinear dynamics tool for spatio-temporal dynamical systems and can be used for bifurcation detection and analysis as well as dimension and degree of complexity estimates. Simple examples are given to illustrate the theory. In particular, we describe a Hopf bifurcation occurring in time showing how the system complexifies spatially and temporally complexifies. Finally, we describe how the tool presented in this paper is ideal for analysis and compaction of experimental data obtained by simultaneous measurements at multiple locations such as laser scanning techniques, image processing of visualization and particle image velocimetry

On The Hidden Beauty of the Proper Orthogonal Decomposition

The Politics of Heresy: The Modernist Crisis in Roman Catholicism

A method and associated apparatus for initiating and guiding an electrical discharge arc. This method preferably comprises the steps of: providing a laser beam through a predetermined gas comprising molecules amenable to vibrational excitation by a laser beam so as to cause vibrational excitation of the molecules and to define a beam path in a direction of desired electrical discharge; and propagating an electrical discharge arc so as to intersect the beam path, whereby the electrical discharge arc is directed along the beam path.

Method and apparatus for initiating, directing and constricting electrical discharge arcs

There are two important trends that are currently taking place in the forming of sheet metal into automotive body components. One of these trends is the substitution of aluminum sheet alloys for steel. The other trend is the use of tailor welded blanks. Currently, there exists strong motivation for research to combine these technologies in order to produce tailor welded aluminum blanks. The focus of the current study is to develop welding procedures for autogenous CO2 (continuous mode) and Nd:YAG (continuous and pulsed mode) laser beam welding of 6111-T4-aluminum alloy. The mechanical and microstructural characteristics of the welded joints were evaluated using tensile tests, microhardess tests, optical microscopy, and chemical analysis. Results indicate that this alloy can be autogenously laser welded with full penetration, minimum surface discontinuities and little if any loss of magnesium through vaporization from the fusion zone. The total elongation (all weld metal) in the longitudinal direction for ...

CO2 and Nd:YAG laser beam welding of 6111-T4 aluminum alloy for automotive applications

Fatigue analysis of laser welded lap joints

Conditions were determined for consistent coupling of a CO2 laser beam to weld 5182 aluminum alloy sheet. Full penetration butt and bead-on-plate welds on 0.8 and 1.8 mm sheets were performed. Process conditions examined included beam mode, spot size and irradiance, shielding gas flow, and edge quality and fitup. The observed weld quality variations with the different process parameters were consistent with physical phenomena and a threshold irradiance model. Optimal conditions were determined for obtaining consistent welds on 5182 alloy sheets. Formability and tensile tests were performed on the welded samples. All test failures occurred in the fusion zone. Reduction in formability and tensile strength of the welded samples are discussed with respect to weld profiles and process parameters.

Charles E. Albright

Papers

The Politics of Heresy: The Modernist Crisis in Roman Catholicism

Method and apparatus for initiating, directing and constricting electrical discharge arcs

CO2 and Nd:YAG laser beam welding of 6111-T4 aluminum alloy for automotive applications

Fatigue analysis of laser welded lap joints

Laser beam welding of 5182 aluminum alloy sheet