Cast Al Alloy Research Articles

Experimental and theoretical studies on thermo‐mechanical fatigue test for aluminium cast alloy

AbstractEvaluation of the thermo‐mechanical behaviour and prediction of the service life of cast aluminium alloys are important for the design of automobile engine cylinder heads. In this study, cast Al alloy specimens are extracted from cylinder heads and subjected to in‐phase thermo‐mechanical cyclic loading. The hysteresis curves related to stress and strain were recorded under the individual thermo‐mechanical loading conditions. The number cycles to failure corresponding to multiple mechanical strain and temperature ranges were obtained. It is found that the cyclic stress amplitude decreases and the cyclic softening rate increases with increasing maximum temperature rise. A modified fatigue‐creep model based on energy conservation has been developed for prediction of the fatigue life of cylinder heads. The proposed method shows good agreement with the well‐established Ostergren model and low standard deviations. In summary, the proposed method described in this study provides an option for prediction of the thermo‐mechanical behaviour of metals.

Modelling the temperature change of bifilm defects in Al cast alloys

Double oxide films (bifilms) are significant defects in the casting of light alloys, and have been shown to decrease tensile and fatigue properties, and also increase their scatter, making casting properties unreproducible and unreliable. Recent research has suggested that the nature of oxide film defects may change with time, as the air inside the bifilm would react with the surrounding melt leading to its consumption, which may enhance the mechanical properties of Al alloy castings. It was suggested that in a pure Al melt, oxygen within the bifilm atmosphere would be consumed first to form alumina, then nitrogen would react to from AlN. A CFD model of the heat distribution associated with the reactions between the interior atmosphere of a double oxide film defect and the surrounding liquid alloy suggested that highly localized increases in temperature, up to 5000, could occur, over a scale of a few hundred micrometers. Such localized increases in temperature might lead to change the nature of the bifilm causing it to be less harmful to the properties of Al cast alloys.

Reliability of a high-pressure die cast Al alloy radiator

The resistance to pressure of a diecast AlSi11Cu2(Fe) alloy radiator has been studied at various holding temperatures. A recently developed method to seal the bottom opening of the radiator element has been presented and its reliability has been even evaluated. Three failure modes are observed during burst testing in the temperature range 40–100 °C, i.e. oil leakage at the interface between the radiator element and the plug, rupture of an element and detachment of the plug from the bottom opening. The main failure mechanism is attributed to the fracture of the radiator element, while the detachment of the plug occurs only at higher temperature; very few leakage failures occur. In the considered experimental range, the temperature exposure affects the burst pressure of the radiator. The failure probability of radiator can be described by three-parameter Weibull distribution, which has evidenced the reliability of the described sealing system.

Application of pulsed Yb: Fiber laser to surface treatment of Al alloys for improved adhesive bonded performance

Surface treatment of the Al surface by pulsed Yb: fiber laser has proven to be effective in improving the adhesive bonded performance of sheet Al substrates. This study was conducted to expand the initial investigation to include sheet, extrusion, and cast Al alloys and measure the effect of laser ablation treatment on the bond strength both in ambient and after water soak. It is found that laser ablation treatment improved the joint strength for all three Al alloys through modification of the surface characteristics and exceeded the target bond strength. Moreover, the results after water soak support the conclusion that the laser ablation treatment exhibited a significant improvement in corrosion resistance of the adhesive-bonded Al joints compared to as-received condition and resulted in the required cohesive fracture mode even after water soak. The reason for this is attributed to the retarding effect of rough laser-ablated surfaces on water diffusion along the bonding interface of laser-treated joints. Besides, the improvement of laser ablation treatment on joint strength before and after exposure increases with the laser fluence. The optimized laser fluence for all three Al alloys is 26.3 J/cm2, which is attributed to a higher degree of laser-induced surface modifications.

Performance of europium in microstructural modification of high strength lightweight aluminum components

Even though all rare-earth elements are within the atomic radii range of Impurity Induced Twinning Model, Europium (Eu) is the only one capable to fully modify the plate like eutectic silicon into fine fibrous morphology. Nevertheless, quantitative information on the microstructural features and mechanical properties of the Eu modified cast Al alloys seems to be scarce. In view of the fact that the process variables alter the microstructures of the casting Al alloys, a study was conducted on the microstructural features of Eu modified A360 Al alloys in order to correlate the parameters such as type and amount of microconstituents and defects to the strength and fracture resistance of the developed alloys. To attain the optimum properties of the cast Al alloys in terms of the strength and fracture resistance, SDAS values are required to be minimized. High cooling rate scale down the dimensions of the Si particles and intermetallics and therefore improve the mechanical properties and fracture resistance of the alloy.

Dry Sliding Wear Behaviour study of Alumina-silicate Short Fiber Reinforced AA2014-Al Alloy composite

Abstract In this study, short alumina-silicate fiber reinforced AA2014 Al-alloy matrix composite was prepared through squeeze infiltration technique. Dry sliding wear behaviour of synthesized composite was carried out using pin on disc under varying applied loads (20-60 N), velocities (2 and 4 m/s) and compared with that of squeeze cast and gravity cast Al-alloy. The wear-response of the investigated materials has been explained on the basis of microstructures, wear surface heating and wear-mechanisms. The wear mechanism in composite has been explained schematically with supporting wear surface and subsurface micrographs. It is interestingly noted that the composite suffers from relatively higher coefficient of friction, the wear rate and frictional heating as compared to the alloys, irrespective of applied load and sliding speed.

Surface strengthening aluminum alloy by in-situ TiC-TiB2 composite coating

An integration technology was employed to prepare TiC-TiB2 strengthening coating on aluminum alloys, with the combination of Self-propagating high-temperature synthesis (SHS) and Vacuum-expendable pattern casting (VEPC). During the VEPC process, the Ti-C-B4C-TP SHS reaction was ignited by molten Al alloy, resulting in the simultaneous obtainment of TiC-TiB2 SHS coating with the cast Al alloy. Specifically, Teflon (PTFE) as reaction promoter was introduced into the SHS system to guarantee the reaction to be ignited successfully. With 3.8 wt% PTFE addition, homogeneous and dense TiC-TiB2 coating microstructure was obtained. Compared to the matrix, the hardness of the surface coating increased from 80 HB to 284 HB. And, the weight loss decreased from 533 mg to 52 mg at load of 20 N, indicating the significant improvement of wear resistance. In addition, a comprehensive bonding strength of 160 MPa was achieved. The proposed method for preparing hard coating on Al alloys broadens their industry application, where higher hardness and better wear resistance are required.

(Invited) Alumina Nanotubes Formed By Anodization of Aluminum Cast Alloy

Anodic porous alumina film, a typical self-ordered nanohole material formed by anodizing aluminum in an appropriate acidic solution, is used as a starting material of nanofabrication of functional devices besides a corrosion resistant surface oxide. In contrast to anodic titania nanotubes, anodic porous alumina is generally compact without spacing between the cell boundary. The tubular shape of anodic titania is suggested to be resulted in enrichment of fluoride between cells which is originated from electrolyte and more soluble than anodic titania. In the case of aluminum, it is reported that enrichment of only sulfate or ethylene glycol from electrolytes produces alumina nanotubes by anodization. In the present paper, the formation mechanisms of alumina nanotubes by anodization of Al cast alloy caused except the electrolyte origin will be discussed. STEM image of vertical cross section prepared by ion-milling of the anodic film, which was formed on 99.99 % pure aluminum in oxalic acid at 160V, indicated close-packed hexagonal cell arrays with small voids of 15-20 nm at the triple cell points. Dark field STEM image clearly revealed a bright particle in the each void suggesting the presence of a heavy metal because of Z-contrast. By EDX point analysis, Cu enriched particles were found in the voids at the triple cell points. Nevertheless, in the case of anodic film formed at the similar condition on AC8A cast alloy including 0.97 % of Cu, tubular cells with the space of approximately 50 nm between cell boundary were formed unlike the case of pure aluminum including 60 ppm of Cu. Numerous branching of pores were also observed. EDX mapping revealed that Si was enriched in the outer layer of the cells and Cu was enriched at the area near the cell boundaries. Therefore, it is deduced that enrichment of Cu at the cell boundaries produces the tubular cells by accelerating oxide dissolution in addition to the electric breakdown accompanied by severe gas evolution that resulted in void formation at the triple cell points.

Mo Addition to the A354 (Al–Si–Cu–Mg) Casting Alloy: Effects on Microstructure and Mechanical Properties at Room and High Temperature

Cast aluminum alloys are widely used in the automotive field for the production of complex engine parts. However, the mechanical properties of heat-treatable alloys (e.g., Al–Si–Mg or Al–Si–Cu–Mg) are negatively affected by prolonged exposure to temperatures higher than about 200 °C. To date, several researchers have proposed the addition of alloying elements, such as Sc or Hf, for enhancing the high temperature behavior of cast Al alloys, while Mo has not been widely investigated. The present study aimed to assess the effects of Mo addition on microstructure, mechanical properties, and thermal stability of the A354 alloy. Samples of A354 alloy with different amount of Mo (in the range 0.1 to 0.8 wt %) were produced. The casting conditions and heat treatment parameters were optimized by means of optical and scanning electron microscopy, thermal analysis and hardness tests. Tensile tests highlighted that Mo induces a moderate increase of yield strength at room temperature (about 10%), but no appreciable improvement in the performance of the alloy at 250 °C was observed.

Numerical Simulation and Process Optimization of Vacuum Investment Casting for Be–Al Alloys

Be–Al alloy castings are widely used in aviation, aerospace and marine industries due to their excellent comprehensive properties. To improve the quality of products, vacuum investment casting of a bracket casting of Be–Al alloys was simulated using the finite-element method and the evolution of the flow field and temperature field as well as the formation of shrinkage porosity were simulated. The simulated results of positions of shrinkage porosity agreed well with the experimental results. The optimized casting parameter with ceramic shell preheat temperature of 500 °C and pouring temperature of 1300 °C was determined by numerical simulation. After the process optimization, a high quality Be–Al alloy casting was successfully produced by pouring once.

A comparative study on corrosion and microstructure of direct metal laser sintered AlSi10Mg_200C and die cast A360.1 aluminum

Direct metal laser sintering (DMLS) is an additive manufacturing technique that creates near-net-shape functional components by selectively melting metal powders in two dimensions layer by layer using a high power laser as a heat source. This technique offers to create parts with complex net-shape structures at an affordable cost with the least lead time. The main purpose of this study is to investigate the corrosion behavior and microstructure of AlSi10Mg_200C manufactured using DMLS compared with its die cast counterpart (A360.1 die cast Al alloy). The impact of the alloy’s surface finish, i.e. as-printed surface versus as-ground one, on the corrosion performance was also investigated. Several AlSi10Mg_200C cube samples were additively manufactured through DMLS technique. In addition, the same size cubes were cut from an aluminum A360.1 die cast ingot. The corrosion behavior of the two alloys was analyzed utilizing potentiodynamic polarization testing and electrochemical impedance spectroscopy in aerated 3.5 wt.% NaCl solution to mimic sea water environment at 25 °C. Further, the microstructures and composition of the samples before and after corrosion testing were investigated using Optical Microscopy (OM), Scanning Electron Microscopy (SEM), and Energy Dispersive X-ray (EDX) spectroscopy. The results confirmed that the corrosion resistance of the alloy processed through DMLS was significantly better than the cast counterpart. This was attributed to the fine microstructure produced by DMLS, uniform distribution of the fine Si particles without formation of any intermetallic, due to the extremely rapid cooling and solidification rate during DMLS process and slightly lower Fe and Cu concentration of the AlSi10Mg alloy. In contrast, the A360.1 cast Al alloy samples experienced severe localized corrosion of the Al matrix in the periphery of the Fe containing IMC and Si flakes. The results also highlighted improved corrosion resistance of the as-printed DMLS sample compared with that of the as-ground one.

Effect of grain refinements on the microstructure and thermal behaviour of Mg\u2013Li\u2013Al alloy

The light as-cast Mg–9Li–1.5Al alloys were manufactured and modified by 0.2 mass% Zr, commercial 0.2 mass% TiBor and 0.2 mass% AlSr master alloys. The thermal derivative analysis using UMSA platform was utilised to characterise a crystallisation process. Samples were heated up to 700 °C and then freely cooled down (~ 0.6 °C s−1) to ambient temperature in order to simulate the natural cooling of casts. Dilatometry study was used to identify changes in solid state. The relative elongation of unmodified and modified alloys was measured in the temperature range from 20 to 400 °C, with a heating rate 1.0 °C s−1. The effects of Zr, TiBor and AlSr content on the microstructure of analysed magnesium alloys were investigated. Evaluation of microstructure was identified by light microscope, scanning electron microscopy, X-ray diffraction and energy-dispersive X-ray spectroscopy. The results showed that the addition of TiBor reduced the grain size of Mg–9Li–1.5Al cast alloy from 930 to 530 µm, while the addition of AlSr master alloy reduced the grain size to 480 µm. Moreover, an addition of TiBor and AlSr simultaneously reduced the grain size to 430 µm. The addition of Zr causes a reduction in grain size to 630 μm. The addition of grain refinement causes changes in crystallisation process and variations in the coefficient of linear thermal expansion (CTE).

Room Temperature Mechanical Properties of A356 Alloy with Ni Additions from 0.5 Wt to 2 Wt %

In recent years, the influence of Ni on high-temperature mechanical properties of casting Al alloys has been extensively examined in the literature. In the present study, room temperature mechanical properties of an A356 alloy with Ni additions from 0.5 to 2 wt % were investigated. The role of Ni-based compounds and eutectic Si particles in reinforcing the Al matrix was studied with image analysis and was then related to tensile properties and microhardness. In the as-cast condition, the formation of the 3D network is not sufficient to determine an increase of mechanical properties of the alloys since fracture propagates by cleavage through eutectic Si particles and Ni aluminides or by the debonding of brittle phases from the aluminum matrix. After T6 heat treatment the increasing amount of Ni aluminides, due to further addition of Ni to the alloy, together with their brittle behavior, leads to a decrease of yield strength, ultimate tensile strength, and Vickers microhardness. Despite the fact that Ni addition up to 2 wt % hinders spheroidization of eutectic Si particles during T6 heat treatment, it also promotes the formation of a higher number of brittle Ni-based compounds that easily promote fracture propagation.

Experimental Studies on Al (5.7% Zn) Alloy based Hybrid MMC

In this investigation, an attempt is made to disperse SiC (20-25 microns) and Gr (15-20 microns) in the aluminium alloy having Zn, Mg and coper as major alloying elements. The composite is further subjected to mechanical testing to determine various properties like hardness, tensile strength and wear resistance. The alloy and composite samples were tested in the un heat treated conditions. All the tests were done at the laboratory conditions as per ASTM standards. The Pin-On-Disc tribometer is used to test the two-body abrasive sliding wear behaviour in dry conditions. The wear pattern is analysed by the optical images of worn surface taken in an inverted metallurgical microscope. The calculated density is found to be reducing as the SiC and Gr quantity is increased in the base alloy. The as cast Al alloy was found to be having highest hardness. The introduction of SiC tend to increase the hardness and UTS, since Gr is also introduced simultaneously which tends to reduce the hardness and UTS of composite. The composite having highest quantity of Gr showed superior wear resistance which is mainly because the Gr particulates provide an inbuilt lubricating properties to composite. The analysis of images of worn surface showed the abrasive and delamination pattern of wear. The composites developed in the present work can be used in the automobile and aerospace parts that are light in weight and require self-lubricating properties to enhance the wear resistance.

Production and Mechanical Testing of Aluminium Alloy Based Hybrid Metal Matrix Composite

The present work aims for uniformly dispersing Aluminium Oxide (Al2O3) and Graphite (Gr) particulates in an Aluminium Alloy Matrix to produce a hybrid composite and then to carry out the investigation and analysis of mechanical properties of developed composite. The particle size of Al2O3 and Gr were less than 45 microns. The stir casting technique is utilized to produce the hybrid composite having 2% Al2O3 with 0.5%, 1% Gr and 4% Al2O3 with 0.5%, 1% Gr. The composites were studied for density changes due to reinforcements, hardness, tensile strength and wear behaviour in Non-Heat Treated (NHT) conditions. The tests were done at the laboratory conditions as per ASTM guidelines. The Pin-On-Disc machine is used to test the sliding wear behaviour under dry conditions. The measured density is found to be decreasing as the reinforcement quantity is increased. The as cast Al alloy was found to be having highest hardness and the composites with increasing Gr exhibited lower hardness. The composite tensile strength is observed to be decreased in comparison to base alloy due to the presence of Gr but composite having highest quantity of Gr showed superior wear resistance which is mainly because the Gr particulates provide an inherent lubricating properties to composite. The composites developed in the present work can be used in the automobile and aerospace parts that are light in weight and require self-lubricating properties to enhance the wear resistance.

Production of open-cell Al composite foams by direct casting with silica-gel beads

Open-cell Al composite foams, with the addition of Al2O3 particles, have been successfully produced, using direct casting technique of space holder materials. The amorphous silica-gel (SiO2) beads of 3 mm were employed as a space holder. The ADC12 cast Al alloy was added with 1-5 wt.% Al2O3 particles, prior to casting process. The infiltration of molten Al composites was performed at 750°C for 30 min with a pressure assistance. Elimination of silica-gel beads was achieved, using the solution of hydrofluoric (HF) acid for 10 h, resulting in open-cell foams with a porous structure, replicated to the morphology of silica-gel beads. However, it was found that the foam structure was also slightly damaged during the removal process of silica-gel beads.© 2017 Elsevier Ltd. All rights reserved.Selection and/or Peer-review under responsibility of The 10th Thailand International Metallurgy Conference.

Secondary cast Al-alloys with higher content of iron

The use of secondary aluminium cast alloys can reduce significantly the production costs of a casting, are cheaper and their production requires much less energy and generates less CO2 emissions. But secondary Al-alloys (produced from Al-scrap) contain higher background Fe levels than the primary metal. The article describes the evaluation of Fe-rich phases in secondary AlSi7Mg0.3 cast alloys with amount 0.12; 0.45 and 0.65 wt. % of Fe. Higher content, as 0.3-0.5 wt. % of Fe, causes first of all formation of Fe- phases (needle-like Al5FeSi and skeleton-like Al15(FeMg)3Si2). First of all long and brittle Fe-platelets (needles as they appear in the microstructure) have influence on the formation of porosity and increase the dimensions of the casting defects. In experimental material was observed, as the iron content increases, the volume fraction of Fe-rich intermetallic phase’s increases too. A higher percentage of iron occurred to the progressive lengthening of a needle-like Fe-phase, Al15(FeMg)3Si2 phases was transformed into Al5FeSi phase; average pore sizes gently decreased, but maximal pore size increased.

The Fatigue lifetime of AlZn10Si8Mg cast alloy with different percentage of iron

To increase the proportion of Al-cast alloys in a variety of industrial applications, it appears useful to control their fatigue behavior. In general, that behavior is affected by many factors, such as chemical composition, heat treatment, inclusions etc. The problem with utilization of the Al-scrap as a material for casting the Al-Si alloys lies in the fact that the scrap, unfortunately as a rule, is contaminated with iron. The Fe-rich intermetallics, formed during the solidification process, appear in a great variety of shapes and sizes. The most important are platelets or needles Al5FeSi, because they greatly decrease mechanical and corrosion properties of Al-cast alloys. The effect of the brittle Fe-rich phases on the fatigue properties in the secondary self-hardening AlZn10Si8Mg cast alloys with different percentage of iron (0.150 and 0.559 wt. %) was studied. Microstructure of alloys and the 3D-morphology of phases were analyzed by the optical and SEM microscopy. Rotating bending fatigue tests were realized for a defined number of cycles 3 x 106. The results show that with increasing the content of Fe, the area proportion and the average length of Al5FeSi phases increased a significant influenced on the fatigue life and pores formation.

Effect of Ni addition on tensile properties of squeeze cast Al alloy A380

The influence of transition alloying element nickel to the tensile properties of squeeze cast aluminum alloy A380 as one of the most common used hypoeutectic Al–Si–Cu alloys was investigated. Nickel (Ni) addition varying from 0.5 up to 2.0 wt.% was introduced into A380. The alloyed melt was squeeze cast under an applied pressure of 90 MPa. The results of tensile testing on the Ni-containing A380 alloys show that Ni is an effective additive for improving their tensile properties, in particularly, tensile and yield strengths and resilience at room temperature. As the Ni addition increases from 0 to 2.0 wt.%, the ultimate tensile and yield strengths and resilience rise to 225.40 MPa, 128.04 MPa and 175.90 kJ/m3 respectively. The as-cast microstructures of the squeeze cast conventional and Ni-containing alloys were observed by an optical microscope(OM). Examination of the analyzed microstructures indicates that the complex Ni-containing intermetallic phases forms once Ni addition. The presence of the Ni-containing intermetallic phases should be responsible to the improvement of mechanical properties. Based on the density measurements, it is found that the introduction of 2.0 wt.% Ni into the A380 results in a trivial effect on its density by only 0.5%.

Effects of transition metal additions on double-oxide film defects in an Al–Si–Mg alloy

ABSTRACTDouble oxide film defects have been associated with reduced mechanical properties and increased variability in properties in cast Al alloys. This paper explores the effects of the addition of around 0.4–0.5 wt-% of the transition metals Mo or W to an Al–7Si–0.3Mg alloy (2L99). The variability of tensile properties was significantly reduced, resulting in an approximate doubling of the values of the Weibull modulus of the ultimate tensile strength, and an increase of 10–20% in the Weibull modulus of the %Elongation. Scanning electron microscopy examination of the fracture surfaces revealed the presence of oxide films, as expected, but also found AlN. The mechanism(s) by which Mo or W additions improve mechanical properties has not been established, but the presence of AlN suggested the accelerated consumption of the internal atmosphere of the double oxide film defects, leading to a reduction in their size and hence their deleterious effects.This paper is part of a thematic issue on Light Alloys.