Al Si Eutectic Structure Research Articles

Experimental study on TIG full welding and single pass welding quality of 6061-T6 aluminum alloy sheet

6061-T6 aluminum alloy plate (3 × 150 × 300 mm3) was welded by tungsten inert gas (TIG) welding. The welding process methods are single-pass welding process and full welding process respectively. The effects of different welding processes on the performance of TIG welding 6061-T6 aluminum alloy were compared and studied. The effects of microstructure and precipitation on the microhardness and tensile strength were analyzed by optical microscope, scanning electron microscopy (SEM), Energy Dispersive Spectroscopy (EDS) characterization, electron backscattering diffraction (EBSD) characterization, microhardness and tensile test. The microstructure of the weld zone is mainly composed of aluminum solid solution (α-Al) dendritic structure and Al–Si eutectic structure. Through EBSD characterization analysis, the average grain size of the weld zone of the full welding process and the single-pass welding process is about 45 μm and 55 μm, and the grain size of the heat-affected zone and the weld zone of the two welded joints does not change significantly. The hardness curves of the two welded joints have the same distribution trend, which is roughly 'W' type distribution. In the tensile test, the tensile strength of the single pass welding process is lower than that of the full welding process, and the fracture of the tensile parts is dimple structure, which is ductile fracture. Through analysis and comparative study, the full welding process is better than the single-pass welding process when welding 6061-T6 aluminum alloy sheet.

Strengthening mechanisms and work hardening in a heterostructured cast aluminum alloy under compressive loading: Correlation with nanomechanical properties

The compressive deformation behavior of a high-pressure die-cast Silafont®-36 aluminum alloy was evaluated in relation to the microstructural changes during deformation. No strain rate sensitivity was observed for the alloy compressed at room temperature. The as-cast microstructure consisted of softer primary α-Al dendrites and harder Al-Si eutectic structure, which was well depicted by the difference in the nanohardness values using high-speed nanoindentation mapping. The load-bearing capacity of eutectic Si particles and thermal mismatch enhanced dislocation density strengthening were identified to be the predominant strengthening mechanisms in the alloy, plus a certain degree of Orowan strengthening mechanism. The work hardening capacity of the cast alloy was mainly attributed to the increase in the dislocation density in the softer α-Al matrix, which was further assisted by the presence of eutectic Si particles. The relative increase in the flow stresses also corresponded well to that in the nanohardness values of the α-Al grains with increasing strain levels.

Effect of double-side welding on the microstructural characteristics and mechanical performance of dissimilar AA6061-AA5052 aluminium alloys

In this study, cold metal transfer (CMT) based double-side welding process was employed to weld AA5052-H32 and AA6061-T6 plates having a thickness of 6 mm. The microstructure and mechanical integrity of the weldment was examined systematically. Symmetric and defect free joint with full penetration was achieved. The multiple heating and cooling cycles during CMT welding did not affect the weldment while the microstructure comprised of columnar and equiaxed dendrites and the heat affected zone (HAZ) width was < 50 µm at all interfaces. Precipitates such as Al3Mg2, Mg2Si, and α-Al(FeMn)Si were observed in the fusion zone. Intergranular Al-Si eutectic structure along with few microliquefaction cracks were noticed in the α-Al matrix. The maximum tensile properties for double-side welded joint were 214 MPa and 12.30 % with a joint efficiency of 70.68 %. Tensile specimens underwent ductile fracture in the weaker AA5052-H32 side with confined plastic deformation.

Heterogeneous microstructure and deformation behavior of an automotive grade aluminum alloy

Aluminum alloy is today considered as a prime selection for manufacturing lightweight structural components in the automotive industry to increase fuel efficiency and reduce harmful emissions. The aim of this study was to identify the effect of microstructure and strain rate on the tensile deformation behavior of a high-pressure die-cast Silafont®-36 alloy, with special attention to strain hardening behavior and deformation mechanisms. The alloy consisted of randomly oriented primary α-Al phase and Al–Si eutectic structure in a form of heterogeneous microstructures, with Sr-modified Si particles exhibiting a coral-like fibrous network. The local misorientations in most primary α-Al grains was below 1°, suggesting strain-free grains along with some extent of near-boundary residual strains due to the thermal mismatch between aluminum and silicon. A superior strength-ductility combination was achieved, along with enhanced Young’s modulus and quality index owing to the unique heterogeneous microstructures. The cast alloy exhibited a smooth deformation characteristic with good coordination deformation and strong strain hardening capacity. Strain hardening exponents evaluated via the equations proposed by Ludwik, Hollomon, Swift, and Afrin et al., respectively, showed basically the absence of strain-rate effect from 1 × 10−5 to 1 × 10−2 s−1. During the tensile deformation, crack initiated from the sample surface and propagated through the alternate microconstituents of softer primary α-Al phase and harder eutectic structure.

Effects of Laser-Powder Bed Fusion Process Parameters on the Microstructure and Corrosion Properties of AlSi10Mg Alloy

In this study, the effects of microstructural modifications induced by tuning the laser-powder bed fusion (L-PBD) process parameters on electrochemical stability of the L-PBF-AlSi10Mg alloy are investigated. Three groups of L-PBF-AlSi10Mg samples were fabricated utilizing combinations of L-PBF process parameters for their Upskin layers. The implemented process parameters modifications were found to be not only effective in reducing the as-printed surface roughness of the components, but also led to the formation of cyclic small-large melt pools (MPs) in Upskin layers of the fabricated samples. Such consecutive modification in the size of MPs led to the increased inhomogeneity of the microstructure, contributing to the formation of a coarser intercellular eutectic-Si network, larger grain size, and lower density of low angle grain boundaries. Among all fabricated samples, the sample that experienced the fastest cooling during solidification was found to reveal the highest corrosion resistance and the best passive film stability on its Upskin surface both in naturally-aerated and deaerated 3.5 wt.% NaCl electrolyte, owing to the finer Al-Si eutectic structure that forms along its large MP-boundaries. The as-printed microstructure of the L-PBF-AlSi10Mg was found a dominant factor in determining the necessity of applying post-printing surface polishing procedures to attain better corrosion properties.

Failure Analysis of the Tree Column Structures Type AlSi10Mg Alloy Branches Manufactured by Selective Laser Melting.

AlSi10Mg alloy branches were fabricated by selective laser melting (SLM), and the branches were employed to evaluate their effect on the mechanical properties. When the porous branches were compressed along its building direction, the tree column structures-type AlSi10Mg alloy branches collapsed twice, which had typical elastic, shear, collapse, and densification stages. The compressive stress concentration at the interface between the support and the porous body caused the fracture of the tree column structures-type AlSi10Mg alloy branches. The fracture surface indicated that the prepared tree-type branches were distributed with different shapes of dimples, and the Si content inside the dimples was higher than that of the edge. The morphology of the Al-Si eutectic structure formed by SLM and the stress concentration at the Al/Al-Si-eutectic interface affected the fracture morphology and Si content distribution.

Microstructural evolution and EBSD analysis of AlSi10Mg alloy fabricated by selective laser remelting

This study characterizes microstructural evolution and texture orientation of AlSi10Mg components through selective laser melting (SLM) by adopting different strategies during remelting. SLM selectively melts the powders and solidified layer, generating a moving melt pool and resulting in unique microstructure. The microstructural evolution, grain sizes and the texture orientation of the fabricated samples were investigated using different scanning strategies by optical microscopy, scanning electron microscopy, and electron back-scattered diffraction. Experimental results show that the inter-connected net shape of the AlSi eutectic structure tends to be widen as a result of the increase of the Si precipitation phase. The grain sizes become smaller and produce more subgrains effected by high thermal conductivity of the solidified layer. The average hardness and Young's modulus increased to 2.32 GPa and 93.26 GPa, respectively. When the remelting scanning direction is rotated to 90°, the cellular microstructure comes into domination. Due to the remelting processing, the preferential grain growth orientation is 〈100〉 both along the scanning and building direction, and the crystallographic texture is enhanced. Results show distinct epitaxial growth along the heat flow with <100> orientation can be obtained and hence isotropy is strengthened.

Effect of traveling magnetic field on separation and purification of Si from Al–Si melt during solidification

Separation and purification of the Si crystal during solidification process of hypereutectic Al–30Si melt under traveling magnetic field (TMF) were investigated in the present study. The results showed that under a proper condition the Si-rich layer can be formed in the periphery of the ingot while the inner microstructure is mainly the Al–Si eutectic structure. The intense melt flow carries the bulk liquid with higher Si content to promote the growth of the primary Si phase which is first precipitated close to the inner wall of the crucible with a relatively lower temperature, which resulting in the remarkable segregation of the primary Si phase. The impurity contents of the refined Si can be reduced to a very low level. The typical metallic impurities have removal fraction higher than 99.5%. In addition, there is a significant difference in the P contents between the primary and eutectic Si phases, which might be ascribed to the formation of AlP phase that acts as the heterogeneous nucleation sites. Furthermore, a considerable amount of Fe-containing particles with a size about 100–300nm is found inside the eutectic Si phase, indicating an unintended entrapment of Fe in Si.

Coating of 6028 Aluminum Alloy Using Aluminum Piston Alloy and Al-Si Alloy-Based Nanocomposites Produced by the Addition of Al-Ti5-B1 to the Matrix Melt

The Al-12 pctSi alloy and aluminum-based composites reinforced with TiB2 and Al3Ti intermetallics exhibit good wear resistance, strength-to-weight ratio, and strength-to-cost ratio when compared to equivalent other commercial Al alloys, which make them good candidates as coating materials. In this study, structural AA 6028 alloy is used as the base material. Four different coating materials were used. The first one is Al-Si alloy that has Si content near eutectic composition. The second, third, and fourth ones are Al-6 pctSi-based reinforced with TiB2 and Al3Ti nano-particles produced by addition of Al-Ti5-B1 master alloy with different weight percentages (1, 2, and 3 pct). The coating treatment was carried out with the aid of GTAW process. The microstructures of the base and coated materials were investigated using optical microscope and scanning electron microscope equipped with EDX analyzer. Microhardness of the base material and the coated layer were evaluated using a microhardness tester. GTAW process results in almost sound coated layer on 6028 aluminum alloy with the used four coating materials. The coating materials of Al-12 pct Si alloy resulted in very fine dendritic Al-Si eutectic structure. The interface between the coated layer and the base metal was very clean. The coated layer was almost free from porosities or other defects. The coating materials of Al-6 pct Si-based mixed with Al-Ti5-B1 master alloy with different percentages (1, 2, and 3 pct), results in coated layer consisted of matrix of fine dendrite eutectic morphology structure inside a-Al grains. Many fine in situ TiAl3 and TiB2 intermetallics were precipitated almost at the grain boundary of a-Al grains. The amounts of these precipitates are increased by increasing the addition of Al-Ti5-B1 master alloy. The surface hardness of the 6028 aluminum alloy base metal was improved with the entire four used surface coating materials. The improvement reached to about 85 pct by the first type of coating material (Al-12 pctSi alloy), while it reached to 77, 83, and 89 pct by the coating materials of Al-6 pct Si-based mixed with Al-Ti5-B1 master alloy with different percentages 1, 2, and 3 pct, respectively.

Separation and purification of Si from solidification of hypereutectic Al–Si melt under rotating magnetic field

A low-cost and high-efficiency method to purify Si directly from cheap MG–Si at low temperature was proposed and demonstrated in this paper, which used power frequency rotating magnetic field (RMF) to separate the primary Si from a hypereutectic Al–Si alloy and was followed by the acid peeling. The separation mechanism was based on the flow characteristic of melt under RMF and the cooling condition of the liquid metal. A Si-rich layer with Si content of 65–59wt% was formed in the periphery of alloy, while the inner microstructure of the alloy was mainly the Al–Si eutectic structure. The refined silicon was collected after aqua regia leaching, and had much fewer typical impurities (Fe, Ti, Ca, B, P) than those in MG–Si, and the metallic impurities besides Al had removal fraction higher than 98%, which is mainly ascribed to the segregation effect of Al-30Si alloy during solidification under RMF.

Heat resisting property of Al coated steel sheet by sputtering

Al coated steel sheets are being used for heat resisting application such as muffler for automobile, fuel tank, microwave oven, and combustion chamber parts. These are commercially produced by hot-dip galvanizing process and their heat resisting properties are depending on their processes. In this study, Al coated steel sheets are fabricated by sputtering process in order to compare their properties with the ones of galvanizing.Hot-dip Al coated steel sheet (HACSS) showed a typical solidified structure of Al–Si alloy; primary Al dendrite and Al–Si eutectic structure. Intermetallic compounds were found between the coating layer and the steel substrate. On the other hand, sputtered Al coated steel sheet (SACSS) represented a well-mixed structure of Al–Si. No intermetallics were observed. Heat resistance tests were carried out at 450 °C and 500 °C. HACSS was discolored at 450 °C, but SACSS at 500 °C. In this study, heat resistance experimental results are analyzed and discussed based on their microstructures of non-ferrous/ferrous metal hybrid system.

Metallurgical and mechanical investigations of aluminium-steel butt joint made by tungsten inert gas welding–brazing

Dissimilar metals of 5A06 aluminium alloy and SUS321 stainless steel were butt joined by tungsten inert gas welding–brazing with BJ380A filler metal and modified non-corrosive flux. The interface in seam/steel is made up of two kinds of intermetallic phase layers, τ5-Al7Fe2Si phase in the seam side and θ-FeAl3 phase in the steel side. The granular phase in welded seam is CuAl2, and the lath shaped phase is τ6-Al5FeSi. In the fusion area, the chainlike phase is Al–Si eutectic structure, and the block-like phase is Al6(Fe,Mn). The tensile strength of the butt joint reaches 125 MPa, and fracture occurs at τ5-layer, with highest hardness value of 950 HV. The present joint without coated layer can reach the same level to those with coated layer.

Structure of in situ Al/Si functionally graded materials by electromagnetic separation method

The aim of this paper is to investigate the structure of in situ Al/Si functionally graded materials by electromagnetic separation method. The research shows that the structure of Al/Si (hypereutectic) sample produced by this method changes from Al–Si hypereutectic structure with a great number of primary Si particles to Al–Si eutectic structure to Al–Si hypoeutectic structure with a great number of primary Al dendrites from one side of the sample to the other. Moreover, the hardness of the sample and the volume fraction of primary Si particles have gradient character in the sample.

In situ multi-layer functionally graded materials by Electromagnetic Separation method

This paper proposes a new technique of in situ multi-layer functionally graded materials (FGMs) by Electromagnetic Separation method using alloy with two or more kinds of primary particles formed in different temperature ranges. In situ three layers FGMs were produced successfully by Electromagnetic Separation method using the alloy with nominal composition Al–22% Si–3.9% Ti–0.78% B. The three layers are respectively the layer of the primary ternary intermetallic compound Al–Si–Ti particles with rich Si, the layer of the primary Si particles, and the layer of the Al–Si eutectic structure. The reason why these three layers appeared under the electromagnetic field is that the first primary Al–Si–Ti particles with rich Si, the second primary Si particles and the Al–Si eutectic structure are formed in different temperature ranges. In the produced samples, interfaces between two layers are gradually transitional in the microstructure.

YAG laser cladding of an Al-Si alloy onto an Mg/SiC composite for the improvement of corrosion resistance

Magnesium metal–matrix composites (MMCs) show great potential for industrial applications. But galvanic corrosion between magnesium matrices and the reinforcing constituents is a major concern when using these materials. Laser cladding onto an Mg/SiC composite was carried out for the enhancement of corrosion resistance in the present study. Results show that laser parameters, especially scanning velocity, have significant influences on both the microstructure and the corrosion resistance. When laser power was kept at 500 W, the laser-clad coating at 8 mm s −1 displayed three layers, i.e. the undiluted layer, the diffusive layer and the interfacial layer. Increasing scanning velocity to 10 mm s −1 caused the elimination of the diffusive layer whilst decreasing scanning velocity to 5 mm s −1 induced the absence of the undiluted layer. An increase of laser power to 600 W resulted in rough surface and porosity in the coating. The undiluted layer has a fine Al–Si eutectic structure and the diffusive layer consists of aluminium, Al–Si eutectic and Mg 2Si phase. The corrosion resistance of the Mg/SiC composite has been significantly improved by using YAG laser cladding treatment, especially, at a scanning velocity of 10 mm s −1.

Effect of antimony on the growth kinetics of aluminium-silicon eutectic alloys

On treating aluminium-silicon alloy with 0.2 wt% Sb, it was revealed that antimony refines the eutectic structure by reducing the interflake spacing rather than acting as a modifier. The growth mechanism is similar to the unmodified Al=Si flake structure, giving the relationships of the type ΔT=K1V0.51 and λ=K2V−0.4, where K1 and K2 are constants at high solidification rate, the transition from flake to fibre is observed. However, this transition occurs at lower velocity compared to quench modification of the pure alloy. The high magnitude of undercooling measured with the antimony-treated alloy is attributed to constitutional undercooling, which leads to extra refinement of the Al-Si eutectic structure.

Microstructural characterisation of sand cast aluminium alloy A356–SiC particle metal matrix composite

The microstructure of a cast aluminium alloy A356 reinforced with 15 vol.-%SiC particles has been investigated using analytical microscopy. It is shown that the morphology of the silicon phase, as well as that of the Al–Si eutectic structure, which are the features of this alloy system, are dramatically changed by the presence of the SiC particles. Significant effects of grain refinement werefound to occur not only on the primary aluminium grains, but also on the primary and eutectic silicon phases. Twinning and dislocations were often observed within that silicon phase which was situated adjacent to the SiC particles. Microcracks were also observed at the SiC/silicon interface. The presence of such microcracks suggests that a stress concentration had developed at the silicon/SiC particle interfaces, probably as a result of the thermal expansion mismatch occurring between the silicon and SiC particles. The microcracks which consequently develop are formed as a result of the poor silicon–SiC particle bonding. Other intermetallics, notably Mg2Si and FeSiAl5, which exhibit cubic and tetragonal symmetries respectively, were also identified as being present in the microstructure.MST/1460

Microstructural studies of aluminium-silicon alloy reinforced with alumina fibres

The microstructure of an alumina fibre reinforced Al-7wt% Si alloy has been investigated. It was shown that the Al-Si eutectic structure which characterized this alloy was markedly changed by the presence of the fibres, with coarsening of silicon particles and a reduction in primary aluminium grain size. The coarse silicon particles exhibited twinning but no orientation relationship with the aluminium. Fine silicon precipitates were also present and these had a cube-cube orientation relationship with the aluminium lattice. Lath-like intermetallics, FeSiAl5 and FeSi2Al4 with monoclinic and tetragonal structures, were identified which existed in equilibrium and had the epitaxial relationship (001)mono//(001)tet and [100]mono//[100]tet. The iron was a contaminant introduced in the course of composite fabrication. Dislocations were a common feature of the aluminium matrix, with a typical density of ∼4×107mm−2. Nevertheless, dislocation hardening of the metal matrix was not detected. No evidence of Mg2Si precipitates in the metal matrix was found, but the small addition (0.2wt%) of magnesium to the alloy was discovered to segregate at the fibre-aluminium interface. This segregation was believed to result in improved wettability of the two constituents, encouraging the formation of a strong fibre-matrix bond, and producing desirable properties of the composite in the transverse direction.