ASM Specialty Handbook Aluminum And Aluminum Alloys.27 [VERIFIED]
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Heat-treatable aluminum alloys are those whose mechanical properties may be improved by means of a specific heat treatment. The T6 heat treatment process involves three stages, namely, solution heat treatment, quenching and aging. The purpose of the solution heat treatment is to place the maximum amount of hardening solutes, such as Mg, into solid solution in the aluminum matrix [8,9,10].
The most commonly used aluminum alloy for automotive engine blocks is 319, which possesses good strength and castability. In this research, 319 Al alloy engine blocks were analysed in the as-cast, heat-treated and service-tested conditions. Extensive microscopy and hardness measurements were carried out on samples extracted from top to bottom along the interbore region of each cylinder. The results suggest that a variation in cooling rate along the cylinders caused a refinement in microstructure at the bottom of the cylinders. Although the morphology of the secondary phases changed, the increased cooling rate did not lead to the formation of different secondary phases, which is indicated by the fact that no significant difference in hardness of the secondary phases was observed at the top and bottom of the cylinder. Furthermore, the results from nanoindentation indicate that Al2Cu has a stronger bond with the matrix compared to Si and Al17Fe3.2Mn0.8Si2.
Due to its popularity and high crack sensitivity, 6061 aluminum alloy was selected as a test material for the newly developed double-sided arc welding (DSAW) process. The microstructure, crack sensitivity, and porosity of DSAW weldments, were studied systematically. The percentage of fine equiaxed grains in the fully penetrated welds is greatly increased. Residual stresses are reduced. Porosity in the welds is reduced and individual pores are smaller. It was also found that the shape and size of porosity is related to solidification substructure. In particular, a weld metal zone with equiaxed grains tends to form small and dispersed porosity, whereas elongated porosity tends to occur in columnar grains.
Powder metallurgy (PM) is a production method that offers manufacturers great advantages overother manufacturing processes. Little changes in the production steps of powder metallurgy methodsuch as powder manufacture, powder processing, pressing, sintering affect the properties of the finalproduct significantly. Aluminum alloys are second most used alloy in the engineering applications.Nowadays some parts in the automotive sector are produced with aluminum PM alloys. In the future,it is expected that more Al-PM parts will be produced with the development of new high strengthAl based PM alloys. In this study, information about the production of the Al-PM parts is given andsome examples about the sintering of Al-Cu, Al-Si and Al-Mg PM alloys from the relevant literatureare presented. Properties of the various sintered PM Aluminum alloys are highlighted.
This paper will cover each of the four areas by discussing, in limited detail, the impact each has on the interface from which the anodic oxide originates and grows. Theoretical scientific reasons for why the problems occur and why most solutions succeed and some fail are followed by case studies that present actual problems and practical solutions based in the scientific background. The limitations as to what can be done from an anodizing standpoint to overcome the metallurgical condition of a cast substrate are presented not as an excuse, but as a call for understanding and communication between metal finishers, component designers who would like to use die castings, and the foundries who pour the castings in order to optimize product and process and to increase the use of anodized cast aluminum components.
Sand, Permanent and Semi Permanent Mold, Die Casting, and other related methods are all utilized today to provide cast aluminum product. The method of choice usually depends upon component size and design, lot size, and alloy requirements. Of these methods, die casting accounts for almost 70% of the total cast aluminum products available worldwide.
Figure 1: Examples of components die cast from alloy AlMg9 (similar to alloy 520), with corresponding microstructure (right). Multiple phases and intermetallic compounds are present throughout the microstructure as Mg2Si precipitates, hypoeutectic silicon and a fine network of Mg5Al8. When non- aluminum alloy constituents intersect the surface, they can interfere with the anodizing reaction.First and foremost, cast alloys are formulated for strength, hardness, and resistance to wear and fatigue. In aluminum casting operations, these properties are produced metallurgically two ways: (1) by solid solution hardening; that is: by the substitution of aluminum atoms with alloying atoms in the aluminum crystal structure and (2) by precipitation hardening: the dispersion of second phase constituents or elements in solution and precipitating them out as small intermetallic compounds, incoherent with the microstructure, which inhibit material deformation. Cast components have limited ductility and can be brittle; therefore, castings are not usually meant for subsequent deformation processing. Other than minimal finishing processes such as machining, a casting is typically produced to function near net shape.
Because cast components are produced to function near net shape, castings can be alloyed beyond what is typical for wrought products; that is, additions of other elements are at a higher per cent than the additions for alloys intended for extruded, rolled or deep drawn product (up to 16% total alloy content for castings vs. up to 8% for wrought alloys). As such, cast alloys are metallurgically more complex than their wrought counterparts; increased alloy additions produce correspondingly higher levels of solution phases, intermetallic compounds and precipitates. Castings, therefore, in addition to their strength and fatigue resistance, exhibit more complex surfaces, with less free aluminum, which make them more difficult to anodize. See Figure 1.
A system of four-digit numerical designations incorporating a decimal point is used to identify aluminum and aluminum alloys in the form of castings and foundry ingot. The first digit indicates the alloy group.10 Table I presents the US cast aluminum alloy designation system and the available product forms. Because die castings are primarily cast from the 300, 400 and 500 series designations, the following discussions will focus on these groups in particular.11 Table 2 presents the compositions of some commonly specified aluminum die cast alloys and their most similar European and Japanese designations.
300 Series: Silicon, with added Copper and/or Magnesium: The 300 series die castings are the most commonly produced and the highest-volume-usage alloys. Because they are comprised of multiple primary alloying elements, in addition to aluminum, the 300 series alloys exhibit the most complex microstructures and therefore present the most complex surface to the anodizing electrolyte.
Copper, as an alloy addition to aluminum castings, increases fluidity and decreases the surface tension of the molten pour and aids in producing a casting that is free of hot shortness and porosity. Within the microstructure, copper refines the grain size; that is, the presence of copper in the microstructure prevents excessive grain growth during cooling and heat treatment.
400 Series: Silicon: These alloys are based on the binary aluminum-silicon phase diagram and contain from 5% to 12% Si. Alloys with these compositions find many applications where combinations of moderate strength, high ductility and impact resistance are required. The Al-Si system is a simple eutectic with limited terminal solubility and is the basis for the 400 series alloys. The limited solid solubility of silicon in aluminum produces Al-Si compositions that will exhibit approximately 1% Si in solid solution as a continuous phase, and the rest of the silicon will fall out as essentially pure particles that range in size from small particles to large needles and plates. See Figure 2.
Silicon is the alloying element that essentially makes the commercial viability of the high volume aluminum casting industry possible. Silicon content between 4% to the eutectic level of 12% reduces scrap losses, permits production of much more intricate designs with greater variations in section thickness and yield castings with higher surface and internal quality (forms sound outer surface layer), because of this, 400 series castings can be used in applications where pressure tightness is a requirement. These benefits derive from the effects of silicon and aluminum molten mixtures which exhibit increased fluidity, reduced cracking and improved feeding to minimize shrinkage porosity. Alloys with the eutectic composition (Al-12%Si) exhibit highest fluidity during casting.
500 Series: Magnesium: The aluminum-magnesium alloys are essentially single phase binary alloys with moderate-to-high strength and toughness properties. Magnesium enhances the molten pour flow. Best corrosion resistance requires low impurity content in the initial pour, both solid and gas, which is difficult because aluminum is second to magnesium regarding affinity for oxygen. This requirement mandates that 500 series alloys be prepared from high quality metals and handled with great care in the foundry, giving rise to questions about effective recycling. Minor amounts of silicon are added to these alloys to precipitate Mg2Si intermetallic compounds for increased mechanical strength.
High corrosion resistance, especially to seawater and marine atmospheres, is the primary advantage of castings made of Al-Mg alloys. These alloys are also the most readily anodized and yield a favorable appearance after anodizing. The 500 series alloys are suitable for welded assemblies and are the best suited when an aluminum casting is needed for decorative or architectural applications. Aluminum- magnesium alloys also exhibit good machinability. 2b1af7f3a8