Secondary Aluminium Alloys Research Articles

Machinability of recycled aluminum alloys

The use of recycled (hereafter called secondary) aluminum alloys is increasing more and more in light of sustainability as the energy needed for their production is much lower than in the case of the primary alloys and they may have mechanical properties comparable to those of the latter. Most of the secondary aluminum alloys are used to fabricate parts through casting processes, which may need further machining operations to get the part’s final shape. While the mechanical properties of the secondary aluminum alloys have been comprehensively addressed in the literature and correlated to the different intermetallic particles that characterize their microstructure, the same is not true when addressing machinability. In this framework, the paper investigates the machinability of one primary and two secondary aluminum alloys in terms of cutting forces and surface finish after turning trials carried out at fixed cutting parameters. A detailed characterization of the alloys’ microstructure was carried out making use of both optical and scanning electron microscopy to identify the size, morphology, and distribution of intermetallics. The highest cutting force was registered when machining the primary alloy, being characterized by the highest specific cutting energy. The surface damage in terms of tearings induced by cutting was comparable between the primary and secondary alloys. In contrast, the different roughness features that characterize the machined surfaces of the considered alloys can be partly ascribed to the different intermetallics they present. Nevertheless, the surface topography analysis results must be interpreted based on the specific application.

Development of Heat Treatments for Structural Parts in Aluminium Alloys Produced by High-Pressure Die Casting (HPDC)

In this work, we intended to study the effect of heat treatments (T5 and flash T6) on blistering, mechanical properties and microstructure for different parts produced by vacuum-assisted HPDC. These parts were produced with primary and secondary aluminium alloys (AlSi10MnMg alloy and AlSi10Mg(Fe) alloy, respectively). The parts presented blisters for all combinations of temperature (between 360 °C and 520 °C) and stage times (15 and 30 min) of solution heat treatments. However, when subjected to the T5 heat treatment, blisters were no longer visible. With this heat treatment, there was an increase in yield strength of 64% for both aluminium alloys and an increase in UTS of 31% in AlSi10Mg(Fe) alloy and of 24% in AlSi10MnMg alloy, when compared to the mechanical properties in the as-cast state. However, there was a decrease in ductility. The AlSi10Mg(Fe) alloy presented a lot of contaminations (especially iron), which impaired the mechanical properties compared to the primary aluminium alloy, AlSi10MnMg.

Influence of Copper Addition on the Mechanical Properties and Corrosion Resistance of Self-Hardening Secondary Aluminium Alloy AlZn10Si8Mg

Aluminium alloys have a wide range of applications, mainly due to their advantageous strength-to-weight ratio, denoted as specific strength and corrosion resistance. In recent decades, there has been a notable surge in the usage of recycled alloys, attributed to their reduced production costs and emissions. One of the conditions for secondary production is the optimal sorting of used scrap. Once the aluminium scrap has been melted, it is tough to reduce the content of the various additives. Copper is the primary alloying element in some aluminium alloys, which leads to an increased amount of copper in the aluminium scrap. Therefore, it is important to investigate its effect on the properties of aluminium alloys in which it is not commonly present. For this reason, this paper is concerned with the influence of copper on the microstructure and properties of the secondary aluminium alloy AlZn10Si8Mg. Specifically, it compares two melts of self-hardening AlZn10Si8Mg alloys differing in copper content (0.019% and 1.72%). A complex quantitative and metallographic analysis by optical and electron microscopy has been performed. Mechanical properties were investigated by tensile test, Brinell hardness, and Vickers microhardness measurements. The corrosion resistance of the individual melts was verified by the Audi test.

LCA of recycling aluminium incineration bottom ash, dross and shavings in a rotary furnace and environmental benefits of salt-slag valorisation

Recycling aluminium in a rotary furnace with salt-fluxes allows recovering valuable alloys from hard-to-recycle waste/side-streams such as packaging, dross and incinerator bottom ash. However, this recycling route generates large amounts of salt-slag/salt-cake hazardous wastes which can pose critical environmental risks if landfilled. To tackle this issue, the metallurgical industry has developed processes to valorise the salt-slag residues into recyclable salts and aluminium concentrates, while producing by-products such as ammonium sulphate and non-metallic compounds (NMCs), with applications in the construction or chemical industries. This study aims to assess through LCA the environmental impacts of recycling aluminium in rotary furnaces for both salt-slag management routes: valorisation or landfill. It was found that this recycling process brings forth considerable net environmental profits, which increase for all the considered impact categories if the salt-slag is valorised. The main benefits arise from the production of secondary cast aluminium alloys, which is not unexpected due to the high energy intensity of aluminium primary production. However, the LCA results also identify other hotspots which play a significant role, and which should be considered for the optimisation of the process based on its environmental performance, such as the production of by-products, the consumption of energy/fuels and the avoidance of landfilling waste. Additionally, the assessment shows that the indicators for mineral resource scarcity, human carcinogenic toxicity and terrestrial ecotoxicity are particularly benefited by the salt-slag valorisation. Finally, a sensitivity analysis illustrates the criticality of the metal yield assumptions when calculating the global warming potential of aluminium recycling routes.

LOW CARBON FOOTPRINT ALUMINIUM COMPONENTS FOR E-MOBILITY

In the fast-evolving E‐mobility transformation, the circular economy is one of the key factors to make Europe carbon neutral by 2050, together with sustainability, achievable only with a synergic approach, from raw material choice to recycling, through product design for re‐purposing. Secondary aluminium alloys have a twenty times lower carbon footprint than primary metals, leading to significant CO2 savings. Their properties can satisfy engineering targets through optimized product design. Adopting a smart system layout, in which functions are assigned to assemblies, some of the low‐end mechanical properties of secondary alloys can be offset. Design for easy disassembling can then guarantee a selective re‐purposing and, finally, an environmentally friendly recycling of components. Innovative products in this field have been developed and successfully produced by means of an optimized high-pressure die casting (HPDC) technology, adopting low carbon footprint raw materials supplied in alternative to ingot format. In this work, the characterization of a component for e-mobility has been conducted, evaluating both the characteristics of the scrap alloy used to produce the castings and the casting itself. The results demonstrate a fine and high-quality microstructure of the casting, proving the feasibility of the production process using exclusively scrap alloy.

Enhancing the strength and structure of Al–Si alloys for biomedical applications through the addition of Sr and Zr grain refiners on secondary AlSi7Mg aluminum alloys

The biomedical industry needs Aluminium alloys with superior corrosion resistance properties for limited applications. The use of Al–Si alloys is often seen as non-bio-compatible alloys due to their lower corrosion resistance properties. The present study aims to enhance the properties of such Al–Si alloys through modification of the Si phases with Strontium (Sr) and Zirconium (Zr) through grain size modification. The present study included the preparation of an Al–Si aluminium alloy utilizing a mixture of different scraps. To refine the grain structure, variable concentrations of Sr and Zr grain refiners were added to the alloy using a stir-casting process. The qualities, including porosity, density, tensile strength, yield strength, and hardness, were assessed according to ASTM standards. The grain size and distribution of intermetallic compounds were investigated by performing a microstructural examination using scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques, to determine the impact of Sr and Zr. The results demonstrate that the inclusion of Sr and Zr grain refiners effectively enhances the grain structure, leading to enhanced microstructural and mechanical properties of the secondary aluminium alloys. This study contributes valuable insights into optimizing the grain refining process for secondary aluminum alloys, offering potential advancements in their industrial applications, particularly in the biomedical industry, where the demand for high-performance biocompatible aluminum materials is steadily increasing.

Producing Structural High Integrity Castings with Minimum Carbon Footprint with the Comptech-Rheocasting Process

Structural high vacuum die casting has been growing significantly over the past decades. It is typically done with special (primary type) alloys, special melt treatment practices, high vacuum, a carefully engineered die casting process applying many best practices in our industry. Structural die castings are growing in size and complexity and die casting machines are getting bigger and bigger - and those castings are becoming a significant challenge with current technologies. It was now found that Rheocasting - a process of preparing a semi-solid slurry (with 30-45% solid fraction) that is injected slower and in a laminar way into the cavity, can take structural die casting to completely new heights, enable the casting of parts that would otherwise be impossible to cast and at the same time reduce or eliminate some of the current problems of structural die casting. With Rheocasting, lower purity (secondary) aluminum alloys can be used and excellent properties can be achieved as cast and heat treated (T5, T6/7). Rheocasting has had a breakthrough in the telecom and other industries, but it has now been optimized to become an essential tool in the toolbox of making structural castings. This paper shows the developments that lead to the successful series production of a large (about 4’ long) hinge pillar for an Electric Vehicle (EV). It explains the challenges and how they were overcome, and some of the possibilities of the process regarding alloys, heat treatments and achievable properties. It also shows how Rheocasting can help die casters produce more complex (thin and thick walled) and very large castings with the highest integrity. It can replace structural low-pressure permanent mold (LPPM) castings and reduce wall thickness, improve tolerances and make them more economical. Rheocasting can enable die casters to enter this new market of structural castings including Gigacastings, produce parts previously thought impossible to cast (and on much smaller machines than thought), and expand the growing structural die casting market even faster and further.

RESEARCH AND IMPROVEMENT OF THE MECHANICAL PROPERTIES OF SILUMIN AK7ч

Purpose. Research and improvement of the technology of improving the quality of secondary silumins developed by Zaporizhzhya Polytechnic National University. Due to the lack of own production of primary aluminum in Ukraine, improving the mechanical and service properties of secondary aluminum alloys obtained from scrap is an urgent task.
 Research methods. The object of research was the secondary aluminum alloy AK7ч with chemical composition, %: 6.72 Si, 0.05 Cu, 0.08 Mn, 0.32 Mg, 0.02 Zn, 0.01 Ti, from 0.49 to 1 .59 Fe (5 fractions), the rest – Al. To neutralize the negative effect of iron and other impurities on the mechanical properties of the secondary alloy AK7ч, a complex technology (sorting of scrap, refining and modification of liquid metal) was used. The content of the complex modifying additive MK-1 was 0.10%; 0.12%; 0.14%; 0.16% and 0.20%, respectively, with increasing iron content. Yield strength, elongation, and hardness were determined by standard methods at room temperature. Fatigue tests were performed on a magnetostriction machine at a frequency of 18 kHz. Control of the frequency of oscillations was carried out using a frequency meter. The influence of the load frequency on the fatigue characteristics of the alloy was evaluated using the fatigue life curves with a limited endurance limit.
 Results. An increase in mechanical properties, including resistance to destruction at high load frequencies, has been achieved.
 Scientific novelty. New data were obtained on the effect of iron on the fatigue strength of aluminum alloy AK7ч.
 Practical value. The obtained results expand the possibilities of using secondary aluminum alloys. The established dependencies can be used in the optimization of the composition of secondary silumins.

The Fractographic Analysis of Tensile and Fatigue Fracture Surfaces in Secondary A356 Aluminum Alloy with a Higher Concentration of Iron

A significant number of different metals are present in aluminum alloy scrap and waste. Secondary aluminum cast alloys, made by recycling from scrap and waste, have as the main impurity Fe. Fe reduction is a very economically and technologically expensive process and therefore there is a growing interest in researching such materials. Moreover, the higher content of Fe leads to the formation of brittle Fe-rich phases, leading to faster propagation of fracture in castings. Therefore, this study reflected on secondary aluminum cast alloy with a higher concentration of Fe and research their effect on brittle Fe-rich phase formation (in the needle; plate-like form) and propagation of fracture in the castings. This study confirms the increasing amount of needle Fe-rich phases in the melt with higher content of Fe. The increasing amount of such phases leads to the formation of a large number of cleavage fractures on fracture surfaces. Although the cleavage fracture increased, the experimental results show low changes in the properties of all experimental melts.

The Impact of the Minimum Ductility Requirement in Automotive Castings on the Carbon Dioxide Footprint throughout the Useful Life of an Electric Car

There is a trend in the automotive producers to require that foundries use more secondary aluminum alloy ingots to reduce the CO2 footprint of car production. The merits of this trend have been investigated in this study. Results have shown that requiring the use of more secondary ingots while simultaneously reducing the elongation requirement of aluminum alloy die castings is counterproductive, i.e., increases the CO2 footprint of the car over its useful life by not taking advantage of the weight reduction possible. It is recommended that (i) foundries improve their melt handling capabilities to reduce and minimize the entrainment damage made to the melt in the melting and casting process chain, and (ii) automobile producers reduce the weight of die castings by increasing requirements on elongation, to secure a reduced CO2-footprint in the designs, materials usage and life-cycle of cars.

Characterization of Al Alloys Injected through Vacuum-Assisted HPDC and Influence of T6 Heat Treatment

AlSi12(Fe), AlSi10Mg(Fe), AlSi10MnMg, and AlMg4Fe2 die-casting alloys were produced by high-pressure die casting (HPDC) and vacuum-assisted high-pressure die casting (VADC) under a vacuum level of 200 mbar. The chemical composition, hardness, gas and shrinkage porosity, and mechanical properties were analyzed. The parts under study were subjected to a T6 heat treatment. The VADC led to a decrease in the percentage of defects in the as-cast state for all the alloys, due to a reduction in the amount of gas porosities. After heat treatment, the quantity of gas and shrinkage porosities increased. The efficiency and level of vacuum used were not sufficient to improve the mechanical properties in the as-cast state. The ductility of AlSi10Mg(Fe) and AlSi10MnMg alloys was improved after heat treatment; however, the YS and UTS of AlSi10Mg(Fe) did not increase. The primary aluminum alloys presented higher elongation values than the secondary aluminum alloys due to the reduced amount of the needle-like β-Al5FeSi phase.

Effects of Mn addittion, cooling rate and holding temperature on the modification and purification of iron-rich compounds in AlSi10MnMg(Fe) alloy

The use of secondary aluminum alloys in industry is still limited by the high Fe contents in recycled alloys. In general, the Fe-rich intermetallic compounds deteriorate the performance of secondary Al–Si alloys, specially the β-Fe phase. To mitigate the detrimental effects of iron, the influence of diferent cooling rates and holding temperatures on the modification and purification of iron-rich compounds in commercial AlSi10MnMg alloy with 1.1 wt % Fe was studied. According to the results obtained by CALPHAD calculations, the alloy was modified by adding a 0.7 wt%, 1.2 wt%. and 2.0 wt% of Mn. The phase formation and morphology of iron-rich compounds was systematically studied and correlated by different microstructural characterization techniques. The experimental results showed that the detrimental β-Fe phase can be avoided by adding at least 1.2 wt % of Mn at the studied cooling rates. Finally, the effect of different holding temperatures in the sedimentation of Fe-rich compounds also was studied. Hence, the gravitational sedimentation experiments at different holding times and temperatures were conducted to validate the feasibility of the methodology in different processing conditions. The experimental results showed a high Fe removal efficiency up to 64% and 61%, after a holding time of 30 min at 600 °C and 670 °C, respectively. The addition of Mn improved the Fe removal efficiency but not gradually, as the best results were obtained in the alloy containing 1.2 wt % Mn.

Adding Value to Secondary Aluminum Casting Alloys: A Review on Trends and Achievements.

Aluminum is a critical element of the circular economy as it can be recycled several times. Moreover, Al recycling is a more economically and environmentally efficient procedure than the primary Al production from ores. Secondary aluminum alloys are mostly used in casting applications since it is possible to accommodate their chemical composition through secondary manufacturing processes. However, the quality of the alloys may be considerably altered during the different steps of the recycling process. Inadequate waste sorting might result in excessive contamination. Iron is the most dangerous contaminant because it causes brittle and fragile intermetallic phases, which significantly impacts the mechanical characteristics of alloys. In addition, the microstructure of the alloy changes significantly after multiple cycles of remelting. These issues lead to the downcycling of aluminum, i.e., in other words, the reduction in the overall quality of the alloys. Thus, it has been shown that a number of procedures, including ultrasonic melt treatment and microalloying with rare earths, can somewhat alter the shape of the Fe-rich phases in order to reduce the shortcomings of downcycling. However, a solid mechanical characterization is still missing in order to improve the Fe-rich phase alteration.

Effect of Increasing Fe Content on the Fatigue Resistance of Secondary Aluminium Alloy AlSi7Mg0.6

Since the discovery of aluminium, scientists have always seen aluminium alloys as excellent construction materials. They are among the most widely used metals in many industries. Over the last decades, secondary aluminium alloys have received much attention. Recycling aluminium scrap is beneficial for the environment. Furthermore, it requires less energy, so the production costs are lower compared to primary aluminium. The most common obstacle while using secondary aluminium alloys is their increased iron content because it negatively affects their properties. The study aims to widen current knowledge of iron's impact on the fatigue resistance of secondary aluminium alloys.

The Influence of Fe Content on Corrosion Resistance of secondary AlSi7Mg0.3 Cast Alloy with Increased Fe-content

Production of primary aluminium is energetically enormously expensive. The use of secondary (recycled) aluminium, has therefore a high potential to save money and energy while reducing the negative environmental impact of aluminium production. Although the properties of secondary aluminium alloys are generally comparable to those of primary aluminium alloys, the increased Fe content can lead to a significant reduction in the corrosion resistance of these alloys. Secondary (recycled) AlSi7Mg0.3 cast alloy with different iron contents (0.123, 0.454, 0.679 and 1.209 wt. %) in the as-cast and after heat treatment (T6) condition was investigated. The quantitative analysis was focused on the evaluation of the Fe-phases, especially the needle-like Al5FeSi phase. The corrosion resistance was measured by a rapid corrosion test (AUDI test). The corrosion damage of the surface was observed macroscopically. The results show that Fe content higher than 0.454 % has no significant effect on the amount and size of needle-like phases of Al5FeSi. The corrosion resistance is mainly influenced by the size and length of the Al5FeSi phases. Increased Fe content decreases the corrosion resistance of AlSi7Mg0.3 alloy and accelerates the initiation of corrosion.

Effect of Higher Iron Content and Manganese Addition on the Corrosion Re-sistance of AlSi7Mg0.6 Secondary Alloy

The use of secondary aluminium alloys gives manufacturers in many industries the opportunity to produce their products more economically and environmentally friendly. The secondary aluminium alloy production is sustainable in the long term. As aluminium does not lose its excellent properties through recycling, secondary aluminium alloys have the potential to replace primary aluminium in many applications. However, recycled aluminium alloys have the disadvantage of insufficient sorting and thus a higher content of impurities in their chemical composition. The most common undesirable element in Al-Si-Mg cast alloys is iron. It adversely affects mechanical properties, fatigue behaviour and corrosion resistance. The influence of iron can be reduced by the addition of manganese. This paper deals with the effect of manganese on the morphology of Fe-phases and corrosion resistance of AlSi7Mg0.6 secondary alloy with higher iron content (0.75 % and 1.26 %).

Influence of Ti, Sr and B additions on the fluidity of A356.2 aluminium alloy

Nowadays, aluminum alloys with silicon are the most widespread construction materials. To increase the mechanical properties of aluminum alloys, modifying by Sr, Ti, and B are used. However, in the foundries, when using scrap and secondary aluminum alloys, the modifying elements are accumulated in alloys in the form of intermetallic particles that decrease castability. This is because of the modifiers have a short time effect and are not activated when remelting. Hence it is necessary to add the modifiers without reference to intermetallic particles that are exactly presented in the melt. This work investigated the effect of Sr, Ti, and B additions on A356.2 aluminum alloy fluidity obtained by vacuum fluidity test. It was shown that when AlSr10 and AlTi5B1 commercial master alloys are used (up to 0.3 wt.% Sr and 0.5 wt.%Ti), no fluidity decrease is observed. However, adding the same quantity of Ti with the homemade AlTi4 master alloy leads to a considerable fluidity decrease. With the help of scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS), the microstructure and phase composition of master alloys and A356.2 alloy after the addition of mentioned master alloys were investigated. Additionally, Thermo- Calc software evaluated the influence of modifier additions on alloy phase composition and phase transition temperatures. It was established that the influence of the modifier additions on the fluidity of the A356.2 alloy is connected with the shape and size of crystals that contained modifier elements in the structure of the master alloy. When the coarse crystals of that phases are present, these crystals’ incomplete dissolution is possible, inhibiting the free melt flow.

Effect of different chloride environments on corrosion behavior of secondary AlSi7Mg0.6 cast alloy with higher Fe content

Secondary aluminum alloys are materials with higher Fe content. There are currently several studies on the corrosion behavior of casts from metal molds, but sand casts are being forgotten despite being still primarily used in gravity casting. Secondary Al-alloys have exceptional benefits as they are made from scrap and can be cast as thin-walled, which has a positive effect on the lightening of constructions, and on environmental impact. Unfortunately, the Fe is a common impurity but in higher content decrease properties of aluminum casts. The removal of the Fe content is very expensive, and therefore the effect of Fe content in a larger amount is monitored. This work is focused on the corrosion behavior of the heat-hardening aluminum alloys commonly used to produce castings AlSi7Mg0.6 for automotive. The experimental alloy was intentionally contaminated with Fe for reaching the critical amount of Fe in aluminum casts. Metallographic analysis (using optical and scanning electron microscopy, energy dispersive X-ray analysis) was used before corrosion tests. The microstructure of experimental alloys with higher content of Fe contains large Fe-rich phases in the form of needles. These changes in microstructure lead to the formation of a higher amount and size of porosity but the α-phase was not affected. Corrosion properties were examined by three basic corrosion tests: immersion test, potentiodynamic test, and Audi test. Corrosion characteristics of materials were evaluated using a stereo and optical microscope. Corrosion evaluation of the alloys shows the presence of pitting corrosion, which increases with increasing Fe content.

Influence of modification with highly dispersed silicon carbide on the casting properties of the secondary alloy of the Al-Si system

One of the main areas of application of aluminum is the aerospace and transport industries, which are constantly increasing the requirements for the properties of cast products. The use of aluminum as the main material for the manufacture of various parts of vehicles can significantly reduce their weight, which leads to a decrease in fuel consumption. In order to meet the requirements of the modern world, the work considers studies to improve the quality and increase the properties of products from the secondary aluminum alloy AlSi12. Modern technologies for processing liquid aluminum alloy are analyzed. According to the results of an analytical review, it was found that modifiers that affect the size of the primary grain and the shape of inclusions of eutectic silicon are of the greatest interest. It was found that the modification processes do not change the chemical composition of the alloy, but rather contribute to a change in the size and shape of the structural components of the alloy. The paper considers the influence of an ultradispersed SiC modifier with a particle size of up to 200 nm on the casting properties of secondary aluminum alloys: fluidity, linear and volumetric shrinkage. The fluidity was studied in green sand and metal mould. It was found that the addition of 0.1 % SiC improves the fluidity of the secondary alloy from 560 to 630 mm for green sand mould and from 230 to 295 mm for a metal mould due to cleaning from non-metallic inclusions. A further increase in the SiC content to 0.2 % does not lead to an obvious increase in fluidity. The study of linear shrinkage found that increasing the content of the modifier to 0.2 % contributes to its decrease. At the same time, an increase in the pouring temperature of the alloy promotes an increase in the total linear shrinkage, which is associated with the long residence time of the metal in the liquid state. As a result of the rapid crystallization of the melt with additional nucleation centers in the role of which are particles of the ultradispersed modifier, the coefficient of volumetric shrinkage decreases from 28 to 20 %. The proposed technical solutions for the modification of alloys of the secondary alloy AlSi12 can be used in processes that will improve the quality of cast metal products with the economical use of energy resources and materials for its production.

Investigation of mechanical properties of secondary AlSi7Mg0.3 cast alloys before and after corrosion

The casting industry currently use about 35% of secondary (recycled) aluminum and about 65% of primary aluminum to meet their needs. The manufacturer wants to use the secondary aluminum alloys more and more, but these materials have the higher amount of the undesirable elements. The most negative element in such alloys is Fe. Although the corrosion current increased due to the presence of alloying elements in the matrix of aluminum alloys, the higher content of Fe (which led to increasing amount of Fe-rich phases) could affect the corrosion resistance. The basic metallography assessment of experimental materials microstructure confirm the higher amount of Fe-rich phases in secondary alloys. The results of mechanical properties shows that the higher content of Fe (also Fe-rich phases) does not lead to decreasing the mechanical properties. The similar results of mechanical properties were reached after corrosion attack with 3.5 wt. % NaCl. The assessment of corrosion attack confirmed the presence of pitting corrosion on experimental samples, which increase with increasing Fe content.