Al-Based Foams as Permanent Cores in Al Castings: Effect of Surface Skin Thickness and Composition on Infiltration and Core-Shell Bonding

An emerging and still poorly explored application of aluminum foams is their potential use as permanent cores (inserts) in the casting of aluminum alloys. In this context, Al-based foams can introduce a weight reduction, the obtainment of cavities, a strength increase, the ability to absorb impact energy and vibration, acoustic insulation ability, the possibility to simplify the technological processes (no removal/recycling of traditional sand cores), and finally, they can be fully recyclable. Cymat-type Al foams with thin outer skin were used as permanent cores in Al-alloy gravity casting in the present research. Al-foams were characterized in terms of porosity, density, cell wall and skin thickness, surface chemical composition and morphology, and compression resistance. Cast objects with foam inserts were characterized by means of optical microscopy. The preservation of up to 50% of the initial porosity was observed for foam inserts with higher density. Metallurgical bonding between the foam core and the cast metal was observed in some regions.

Microstructural Evolution as a Function of Increasing Aluminum Content in Novel Lightweight Cast Irons

In the context of the development of new lightweight materials, Al-alloyed cast irons have a great potential for reducing the weight of the different part of the vehicles in the transport industry. The correlation of the amount of Al and its effect in the microstructure of cast irons is not completely well established as it is affected by many factors such as chemical composition, cooling rate, etc. In this work, four novel lightweight cast irons were developed with different amounts of Al (from 0 wt. % to 15 wt. %). The alloys were manufactured by an easily scalable and affordable gravity casting process in an induction furnace, and casted in a resin-bonded sand mold. The microstructural evolution as a function of increasing Al content by different microstructural characterization techniques was studied. The hardness of the cast irons was measured by the Vickers indentation test and correlated with the previously characterized microstructures. In general, the microstructural evolution shows that the perlite content decrease with the increment of wt. % of Al. The opposite occurs with the ferrite content. In the case of graphite, a slight increment occurs with 2 wt. % of Al, but a great decrease occurs until 15 wt. % of Al. The addition of Al promotes the stabilization of ferrite in the studied alloys. The hardness obtained varied from 235 HV and 363 HV in function of the Al content. The addition of Al increases the hardness of the studied cast irons, but not gradually. The alloy with the highest hardness is the alloy containing 7 wt. % Al, which is correlated with the formation of kappa-carbides and finer perlite.

Grain characteristics, electrical conductivity, and hardness of Zn-doped Cu–3Si alloys system

The grain characteristics, electrical conductivity, hardness, and bulk density of Cu–3Si–(0.1—1 wt%)Zn alloys system fabricated by gravity casting technique were investigated experimentally using optical microscopy (OM), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The study established the optimal alloy composition and the significance of zinc addition on the tested properties using response surface optimal design (RSOD). The cooled alloy samples underwent normalizing heat treatment at 900 °C for 0.5 h. The average grains size and grains distribution were analyzed using the linear intercept method (ImageJ). The microstructure examination revealed a change in grain characteristics (morphology and size) of the parent alloy by addition of 0.1 wt% zinc. The average grains size of the parent alloy decreased from 12 µm to 7.0 µm after 0.1 wt% zinc addition. This change in grain characteristics led to an increase in the hardness of the parent alloy by 42.2%, after adding 0.1 wt% zinc. The electrical conductivity of the parent alloy decreased from 46.3%IACS to 45.3%IACS, while the density was increased by 8.4% after adding 0.1 wt% zinc. The statistical data confirmed the significance of the change in properties. The result of optimization revealed Cu–3Si–0.233Zn as the optimal alloy composition with optimal properties. The Cu–3Si–xZn alloy demonstrated excellent properties suitable for the fabrication of electrical and automobile components.

A Comparative Study of Fatigue Energy Dissipation of Additive Manufactured and Cast AlSi10Mg Alloy

In this paper, the fatigue energy dissipation of Gravity Casting (GC) and Laser-based Powder Bed Fusion (LPBF) AlSi10Mg alloys under cyclic loading are investigated. The increase in surface temperature related to the energy dissipation effect is decoupled and used to predict the fatigue limits of GC and LPBF AlSi10Mg alloys as being 55.8% UTS and 33.9% UTS, respectively. The energy dissipation rate is obtained by solving the one-dimensional thermal diffusion problem. This energy dissipation is separated into related and unrelated fatigue damage using polynomial function fitting. The energy dissipation related to fatigue damage for LPBF specimens is observed to be higher than that of GC specimens, which indicates worse fatigue performance. The fatigue damage entropy is employed to predict the fatigue life of both GC and LPBF AlSi10Mg alloys, which has a good agreement with the results of a traditional fatigue experiment.

Gravity Casting and Hot Forging of Al-Mg Alloy and Al-Mg Alloy with Fe Added

Al-4.7%Mg alloy with 0, 0.2, 0.4, 0.6 and 0.8% Fe added was cast using a copper mold and an insulator mold. The cooling rates of ingots cast using the copper mold and the insulator mold were 30.6 °C/s and 0.5 °C/s, respectively. The tensile stress and elongation of the ingots cast by the copper mold were superior to those cast by the insulator mold. The addition of Fe did not lead to tensile stress, but the elongation became smaller as the Fe content increased. The elongation of the ingot cast using the copper mold became much smaller on addition of only 0.2% Fe. The tensile stress and elongation were improved by hot forging with 50% reduction. The elongation of the ingots with Fe added was significantly improved by the hot forging. The degree of improvement of the tensile stress and elongation for the ingots cast using the insulator mold was remarkable.

Determination of Mechanical and Tribological Properties of Silicone-Based Composites Filled with Manganese Waste

High-tonnage industrial processes generate high amount of waste. This is a growing problem in the whole world. Neutralizing such waste can be time consuming and costly. One of the possibilities of their reuse is to use them as fillers in polymer composites. Introduction of the filler in polymer matrix causes change in its mechanical and tribological properties. In the article, the effect of introducing fillers from post-production waste, and its effect on changing the physical properties of silicone-based composites filled with manganese (II) oxide and waste manganese residue was investigated. The composites were made by gravity casting. Composites with 2.5, 5, 7.5, and 10 wt% of the fillers were examined. The composite materials were subjected to tests such as: density, hardness, resilience, tensile test, abrasion resistance, and ball-on-disc. Microscopic images showed that, the particles of the fillers are uniformly distributed in silicone matrix with the formation of smaller agglomerates. Such agglomerates introduced a discontinuity in the structure of the polymer material, which caused a decrease in the tensile strength and elongation at break for all tested compositions in comparison with the mechanical properties of the silicone used as the matrix. However, it was found that all silicone-based composites filled with manganese (II) oxide and manganese residue showed a reduction in abrasive wear, compared to the reference sample.

Probability-Dependent Precipitation Strengthening Effect of Anisotropic Precipitate in Al-Mg-Si Alloy Produced by T6 Heat Treatment

This study proposed a constitutive equation to predict the change in yield strength according to the behavior of β″ metastable precipitates, which have a profound effect on strength among materials precipitated during the T6 heat treatment of Al-Mg-Si alloy. The β″ precipitate is a metastable phase before it becomes a β (Mg2Si) precipitate, and is distributed in the form of nano-scale rods in the aluminum alloy matrix. Existing precipitation strengthening models assume the shape of the precipitate to be spherical, and in that case the equation that depends on the Orowan mechanism with the average precipitate size and distribution should dominate. However, precipitates are formed in various shapes and sizes by anisotropic growth. In particular, rod-shaped precipitates are not suitable for the existing precipitation strengthening model. In this study, an Al-Mg-Si alloy was fabricated by gravity casting followed by T6 heat treatment. The new precipitation strengthening effect equation proposes that the β″ precipitate affects yield strength during plastic deformation of the Al-Mg-Si alloy. The proposed precipitation strengthening effect equation probabilistically considers the Critical Resolved Shear Stress (CRSS), which varies depending on the angle between the dislocation and the precipitate, when the dislocation passes through a rod-shaped precipitate.

Effects of Melt Ultrasonic Treatment and Forming Processes on Thermo- Physical Properties of SiCp/Mg and (SiCp+Mg2Si)/Mg Composites

The 10 vol% SiCp/Mg composites were prepared by external addition and stirring-casting method, and the hybrid reinforced (10 vol% SiCp+10 vol% Mg2Si)/Mg composites were prepared by combining in-situ method. The effects of melt ultrasonic treatment (UT) and forming processes on the thermophysical properties of the two composites were studied. The results show that UT can effectively disperse SiC particles in molten magnesium and reduce the casting porosity, while squeeze casting can significantly reduce the porosity of the composites, which can also significantly improve the thermal conductivity. The thermal conductivity (λ) of 10 vol.% SiCp/Mg composites squeeze casted after UT is 135.3 W/(mK) and the average coefficient of thermal expansion (CTE) is 19.95×10-6 K-1 at 293-373 K. Compared with gravity casting, the λ is increased by 17% and the CTE is reduced by 0.8%. The λ of (SiCp+Mg2Si)/Mg composite squeeze casted after UT is 132.4 W/(mK), and the CTE is 18.95×10-6 K-1, which is 27% lower than the CTE of pure magnesium.