Geometrical effects on residual stresses in 7050-T7451 aluminum alloy rods subject to laser shock peening

Laser shock peening (LSP) is an emerging surface treatment technology for metallic materials, which appears to produce more significant compressive residual stresses than those from the conventional shot peening (SP) for fatigue, corrosion and wear resistance, etc. The finite element method has been applied to simulate the laser shock peening treatment to provide the overall numerical assessment of the characteristic physical processes and transformations. However, the previous researchers mostly focused on metallic specimens with simple geometry, e.g. flat surface. The current work investigates geometrical effects of metallic specimens with curved surface on the residual stress fields produced by LSP process using three-dimensional finite element (3-D FEM) analysis and aluminium alloy rods with a middle scalloped section subject to two-sided laser shock peening. Specimens were numerically studied to determine dynamic and residual stress fields with varying laser parameters and geometrical parameters, e.g. laser power intensity and radius of the middle scalloped section. The results showed that the geometrical effects of the curved target surface greatly influenced residual stress fields.

Improvement in mechanical properties of aluminum polypropylene composite fiber

Aluminum particles (Al) were added to polypropylene (PP) in the presence of poly ethylene glycol (PEG) and polypropylene-graft-maleic anhydride to produce composites. The composites were then melt-spun into a mono filament and tested for tensile properties, diameter evenness and morphology. Melt rheological properties of Al/PP composites were studied in linear viscoelastic response regions. It was observed that level of dispersion of aluminum particles within a polypropylene composite fiber could be improved by incorporating polyethylene glycol. The improvement of dispersion led to an improvement in the fibers mechanical properties through a reduction of the coefficient of variation of fiber diameter.

Processing and characterization of porous aluminum

Aluminum foams are now being introduced into automotive industry to reduce weight, to absorb energy in crash situations and to carry sound or heat absorbing functions. In the present study, a novel Spark Plasma Sintering (SPS) process for producing porous aluminums with controlled pore size and porosity and superior energy absorption has been developed. Experimental procedures included the mixing of starting powders, compacting, SPS sintering and leaching out of the space-holding particles. Porous aluminums with various porosities and a wide range of pore size distributions can be produced by the SPS process. Optical microscopy, scanning electron microscopy (SEM) and quantitative image analyses were used to characterize the porous aluminums. Compressive tests were carried out on the aluminum foams to evaluate the mechanical properties.

Compressive behavior and energy absorption of constructed cellular aluminum

The defoThe deformation behaviors and energy absorption characteristics of constructed cellular aluminums were investigated by compressive tests. Constructed cellular aluminum specimens with two kinds of thickness in the cold-pressed panel and various numbers of layers bonded together have been tested. The plateau stress and the energy absorption have been measured and furthermore, the deformation behaviors have been evaluated. Results indicate that superior mechanical properties with constructed cellular aluminums can be achieved when the distribution of material at cell level is properly selected. Excellent energy absorption per unit mass can be obtained by only changing the thickness of the original aluminum sheet.nnation behaviors and energy absorption characteristics of constructed cellular aluminums were investigated by compressive tests. Constructed cellular aluminum specimens with two kinds of thickness in the cold-pressed panel and various numbers of layers bonded together have been tested. The plateau stress and the energy absorption have been measured and furthennore, the defonnation behaviors have been evaluated. Results indicate that superior mechanical properties with constructed cellular aluminums can be achieved when the distribution of material at cell level is properly selected. Excellent energy absorption per unit mass can be obtained by only changing the thickness of the original aluminum sheet.

Processing of fine-grained aluminum foam by spark plasma sintering

Porous materials are now becoming attractive to researchers interested in both scientific and industrial applications due to their unique combinations of physical, mechanical, thermal, electrical and acoustic properties in conjunction with excellent energy absorption characteristics. Metallic foams allow efficient conversion of impact energy into deformation work, which has led to increasing applications in energy absorption devices. In particular, foams made of aluminum and its alloys are of special interest because they can be used as lightweight panels, for energy absorption in crash situations and sound or heat absorbing functions in the automotive industry with the aim to reduce weight to improve crashworthiness, safety and comfort.

Correlation between shoulder flow zone quality and material flow quantity during friction stir welding of thick aluminum section using scroll shoulder tool

The so-called scroll shoulder tool is widely used particularly for thick section friction stir welding (FSW). However, the correlation between its shoulder flow zone weld quality and material flow quantity remains unclear. This information is important for tool design. In the present study, a scroll shoulder tool was used to FSW 20mm thick 6061 aluminum (Al) plates at a range of welding parameters. The pick-up material (PUM) by the scroll was quantified, and the effect of welding parameters and PUM on the shoulder flow zone formation and weld quality was studied. It was found that there is a positive linear relationship between the PUM and weld quality. In order to obtain a defect-free FSW weld produced by the scroll shoulder tool, scroll groove needs to be fully filled by PUM.

Material flow forming the shoulder flow zone using scroll shoulder tool during friction stir welding of thick section aluminum alloys

Scroll shoulder tools are widely used and they do not need to be tilted during friction stir welding (FSW). However, the detailed material flow, which is important for proper scroll shoulder tool design and subsequently for forming the defect-free shoulder flow zone, has not been fully explained. In the present study, features of material flow in shoulder flow zone, during FSW of thick 6061 aluminium (Al) plates using a scroll shoulder tool were investigated. It was observed that there is a simple layer-to-layer banded structure which appears in the bottom portion of shoulder flow zone, but disappears in the top portion of this weld zone. When the scroll shoulder tool is plunged into the workpiece to a determined depth, the workpiece material is extruded by the tool pin, and pushed up into the scroll groove beneath the shoulder forming the pick-up material. During the forward movement of the tool, the central portion of pick-up material was driven downward by the root portion of pin and then it detaches from the tip portion of pin in a layer-to-layer manner to form the weld.

Microstructure and mechanical properties of nitrided and chromized short steel fiber reinforced aluminum based P/M composites

The present investigation is on the microstructure evolution and hardness of powder metallurgically processed Al- 0.5 wt.%Mg base 10 wt.% short steel fiber reinforced composites. The 0.38 wt.% C short steel fibers of average diameter 50µm and 500-800µm length were nitrided and chromized in a fluid bed furnace. Nitriding was carried out at 525°C for 90, 30 and 5 min durations. Chromizing was performed at 950°C for 53 and 7 min durations, using thermal reactive deposition (TRD) and diffusion technique. The treated fibers and resulting reaction interfaces were characterized using metallographic, microhardness and XRD techniques.

Analysis of the current distribution in an aluminum electrolysis cell with copper collector-bar cathode assembly

Understanding the magneto-hydrodynamic forces generated due to the external magnetic field and current density distribution within the cell (current in cell linings) is important in the optimization of cell dynamics. It is well documented that these factors play a crucial role in establishing the metal-pad stability of the cell. Conventional cells use the cathode-collector-bar assembly to carry the current through molten aluminium, the cathode and the steel collector-bar to nearest external bus. The electrical conductivity of the steel is so poor relative to the molten aluminium that the outer third of the collector bar carries the maximum load, which in turn increases the horizontal components of the current within the cell. Previous studies have modelled improvement in the cell instability through external magnetic compensation by redistributing current in the cathode busbar. Very little to date has been published on work to improve the current distribution within the cell. In this work, the current distribution in an aluminium electrolysis cell with copper collector-bar was predicted using finite element modelling. A 2D cross-section of a commercial cell was used under steady conditions of electrical fields in anode, electrolyte, molten aluminium and copper cathode-assembly. Different shapes and sizes of the cathode assembly are also considered to optimise the distribution of current throughout the cathode lining. The findings indicated that the copper-bar of similar size to steel could save voltage up to 150 mV. There is a reduction of more than 70% in peak current density value due to the copper inserts. The predicted trends of current distribution show a good agreement with previously published data.

One-Step synthesis of the pine-shaped nanostructure of aluminum nitride and its photoluminescence properties

An array of pine-shaped nanostructures of aluminum nitride (AlN) was synthesized through direct reaction between Al vapor and nitrogen gas in direct current (DC) arc discharge plasma without any catalyst or template. The as-prepared nanostructure consists of many pine-needle-shaped leaves with conical shape tips. The structure, morphology, and optical property of the nanostructure have been characterized by X-ray powder diffraction, energy-dispersive X-ray spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, Raman spectroscopy, and photoluminescence. A possible growth mechanism of the pine-shaped nanostructure was discussed. Two factors were found to be essential for branched nanostructure growth, i.e., the reaction time and N2 pressure. The photoluminescence spectrum of the nanostructure of AlN revealed an intense emission band, suggesting that there may be potential applications in electronic and optoelectronic nanodevices.