A review of selective laser melting of aluminum alloys: Processing, microstructure, property and developing trends

Magnesium is a lightweight structural metal but it exhibits low ductility-connected with unusual, mechanistically unexplained, dislocation and plasticity phenomena-which makes it difficult to form and use in energy-saving lightweight structures. We employ long-time molecular dynamics simulations utilizing a density-functional-theory-validated interatomic potential, and reveal the fundamental origins of the previously unexplained phenomena. Here we show that the key 〈c + a〉 dislocation (where 〈c + a〉 indicates the magnitude and direction of slip) is metastable on easy-glide pyramidal II planes; we find that it undergoes a thermally activated, stress-dependent transition to one of three lower-energy, basal-dissociated immobile dislocation structures, which cannot contribute to plastic straining and that serve as strong obstacles to the motion of all other dislocations. This transition is intrinsic to magnesium, driven by reduction in dislocation energy and predicted to occur at very high frequency at room temperature, thus eliminating all major dislocation slip systems able to contribute to c-axis strain and leading to the high hardening and low ductility of magnesium. Enhanced ductility can thus be achieved by increasing the time and temperature at which the transition from the easy-glide metastable dislocation to the immobile basal-dissociated structures occurs. Our results provide the underlying insights needed to guide the design of ductile magnesium alloys.

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The origins of high hardening and low ductility in magnesium

Effect of tool rotational speed and pin profile on microstructure and tensile strength of dissimilar friction stir welded AA5083-H111 and AA6351-T6 aluminum alloys

Metallic materials have enabled technological progress over thousands of years. The accelerated demand for structural (that is, load-bearing) alloys in key sectors such as energy, construction, safety and transportation is resulting in predicted production growth rates of up to 200 per cent until 2050. Yet most of these materials require a lot of energy when extracted and manufactured and these processes emit large amounts of greenhouse gases and pollution. Here we review methods of improving the direct sustainability of structural metals, in areas including reduced-carbon-dioxide primary production, recycling, scrap-compatible alloy design, contaminant tolerance of alloys and improved alloy longevity. We discuss the effectiveness and technological readiness of individual measures and also show how novel structural materials enable improved energy efficiency through their reduced mass, higher thermal stability and better mechanical properties than currently available alloys. Structural metals enable improved energy efficiency through their reduced mass, higher thermal stability and better mechanical properties; here, methods of improving the sustainability of structural metals, from recycling to contaminant tolerance, are described.

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Strategies for improving the sustainability of structural metals

Mechanical properties, corrosion behaviors and microstructures of 7075 aluminium alloy with various aging treatments

Driven by the increasing requirements from aircraft producers, Hoogovens Aluminium Rolled Products GmbH, together with Hoogovens Research & Development, has enhanced the property combinations of their aircraft materials. For these types of material, optimised processing routes as well as new alloy chemistries have been investigated. Whilst retaining the strength levels required by the aerospace industry, new processing routes offer major improvements in ductility, toughness, fatigue performance and in reduction of residual stress in large dimension plate and sheet products. A further goal of investigating new alloy chemistries is the trend towards new joining techniques such as welding and brazing for aircraft structures. These new joining techniques require different property combinations compared to the conventional aerospace alloys. In parallel to these improved processing routes and new alloy developments, new ultrasonic inspection techniques have been developed, which are able to predict fatigue performance and residual stress in thick plate products.

Recent development in aluminium alloys for aerospace applications

The aircraft industry is constantly striving for improved materials which enables higher performance at reduced cost. The development of high speed milling machines and improvements in thick plate properties regarding distortion during machining have led to the conclusion that large machined structures can replace forged components and significantly reduce the cost by reducing the number of components and joints. For this reason, Hoogovens Aluminium Rolled Products together with Hoogovens Research and Development, has continued to improve the property balance required for AA7xxx high strength thick plates in aerospace applications. This paper will focus on investigations performed to optimise the process for high strength thick plates. This work contains a careful analysis of the process steps including the measurement of quench rate within thick plates, quench factor analysis, simulation of the effect of changes in quench practice on final properties and modelling work of residual stress to gain the best property balance required for thick plates in aerospace applications. Finally, the improved mechanical properties and the low level of distortion during machining for high strength thick plates will be discussed.

Recent Improvement in High Strength Thick AA7050-Plate

Driven by the increasing requirements from aircraft producers, Corus Aluminium Rolled Products GmbH, together with Corus Research Development and Technology, has enhanced the property combinations of their aircraft materials. For these types of material, optimised processing routes as well as new alloy chemistries have been investigated. Whilst retaining the strength levels required by the aerospace industry, new processing routes offer major improvements in ductility, toughness, fatigue performance and in reduction of residual stress in large dimension plate and sheet products. A further goal of investigating new alloy chemistries is the trend towards new joining techniques such as welding and brazing for aircraft structures. These new joining techniques require different property combinations compared to the conventional aerospace alloys. In parallel to these improved processing routes and new alloy developments, new ultrasonic inspection techniques have been developed, which are able to predict fatigue performance and residual stress in thick plate products.

A. Heinz

Papers

Recent development in aluminium alloys for aerospace applications

Recent Improvement in High Strength Thick AA7050-Plate

New developments in aluminium rolled products for the aircraft and aerospace industry