The growing demand for more fuel-efficient vehicles to reduce energy consumption and air pollution is a challenge for the automotive industry. The characteristic properties of aluminium, high strength stiffness to weight ratio, good formability, good corrosion resistance, and recycling potential make it the ideal candidate to replace heavier materials (steel or copper) in the car to respond to the weight reduction demand within the automotive industry. This paper summarises the recent developments covering aluminium’s use in castings, extrusions and sheet; two specific examples will be given. The first deals with hang-on parts manufactured by Hoogovens Rolled Products Duffel, for which the weight saving potential can be 50%. Currently, the highly formable 5000 alloys are used mostly for inner panel applications, whilst the heat-treatable 6000 alloys are preferred for outer panel applications. This presentation reviews recent developments in aluminium alloys to improve formability, surface quality in both 5000 and 6000 alloys, and the bake hardening response of 6000 alloys. It also indicates the trend to develop a unialloy system to improve the aluminium scrap recycling. The second area deals with brazing sheet. Over the last 10 years there has been an increasing trend to replace copper heat exchangers with ones manufactured from brazed aluminium. Hoogovens Aluminium Walzprodukte Koblenz is one of the world’s leading supplier of aluminium brazing sheet and is in the forefront of developing alloys with the combination of strength, formability, brazing performance and long life required by its customers. Materials have been development for both vacuum and controlled atmosphere brazing. The current status and future trends in aluminium brazing sheet for automotive applications will be presented. Particular emphasis has been placed on the development of long life alloys with superior corrosion performance over the more conventional materials. Using these two examples the technical and commercial aspects of the manufacturing processes of aluminium automotive components and engineering design support of materials producers are illustrated. The essential feature is the close co-operation at all stages between the material’s supplier and the automotive manufacture.

Recent development in aluminium alloys for the automotive industry

Metal-based additive manufacturing, or three-dimensional (3D) printing, is a potentially disruptive technology across multiple industries, including the aerospace, biomedical and automotive industries. Building up metal components layer by layer increases design freedom and manufacturing flexibility, thereby enabling complex geometries, increased product customization and shorter time to market, while eliminating traditional economy-of-scale constraints. However, currently only a few alloys, the most relevant being AlSi10Mg, TiAl6V4, CoCr and Inconel 718, can be reliably printed; the vast majority of the more than 5,500 alloys in use today cannot be additively manufactured because the melting and solidification dynamics during the printing process lead to intolerable microstructures with large columnar grains and periodic cracks. Here we demonstrate that these issues can be resolved by introducing nanoparticles of nucleants that control solidification during additive manufacturing. We selected the nucleants on the basis of crystallographic information and assembled them onto 7075 and 6061 series aluminium alloy powders. After functionalization with the nucleants, we found that these high-strength aluminium alloys, which were previously incompatible with additive manufacturing, could be processed successfully using selective laser melting. Crack-free, equiaxed (that is, with grains roughly equal in length, width and height), fine-grained microstructures were achieved, resulting in material strengths comparable to that of wrought material. Our approach to metal-based additive manufacturing is applicable to a wide range of alloys and can be implemented using a range of additive machines. It thus provides a foundation for broad industrial applicability, including where electron-beam melting or directed-energy-deposition techniques are used instead of selective laser melting, and will enable additive manufacturing of other alloy systems, such as non-weldable nickel superalloys and intermetallics. Furthermore, this technology could be used in conventional processing such as in joining, casting and injection moulding, in which solidification cracking and hot tearing are also common issues.

3D printing of high-strength aluminium alloys

Ecodesign of automotive components making use of natural jute fiber composites

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

Strengthening mechanisms, deformation behavior, and anisotropic mechanical properties of Al-Li alloys: A review

Although heat treatable Al-Si-Mg-based 6000 alloys have become increasingly attractive for automotive skin panel applications, the potential of these alloys is not fully explored in the current automotive body paint bake cycle due to a low temperature and a short duration. In order to improve the bake hardening response in such a cycle, many efforts have been made in past years by means of microstructural modification. This paper presents our recent results in developing pre-aged (T4P) Al-Si-Mg alloys. Two types of processes have been investigated which differ in the holding time between the solid solution heat treatment and the pre-ageing heat treatment, and can be denoted (a) fresh pre-ageing treatment and (b) reversion pre-ageing treatment. The mechanism of microstructural evolution during these processes is discussed, also considering the effect of processing parameters and alloy chemistry on the bake hardening response.

Improvement in Bake Hardening Response of Al-Si-Mg Alloys

Recent Developments in AA6016 Aluminium Type Body Sheet Product

The Effect of Small Particles on Annealed Grain Size and Texture of Al-Mg-Si Alloys

A method for the manufacture of a sheet of an A1MgSi alloy of the AA6xxx type containing Si in an amount of 0.4 to 1.7 wt% and Mg in an amount of 0.2 to 0.9 wt%, comprises the following steps carried out in the following sequence:- (i) cold-rolling of the alloy to the final desired sheet thickness, (ii) solution heat treatment of the sheet, (iii) cooling from the solution heat treatment temperature to below 150 DEG C at a cooling rate of at least 100 DEG C/min. and further cooling to below 50 DEG C, (iv) holding the sheet below 50 DEG C for a holding time of not more than 30 minutes after the end of step (iii), (v) immediately after step (iv), heating the sheet to a predetermined holding temperature within the temperature range 165-185 DEG C, (vi) maintaining the sheet at the predetermined holding temperature for a holding time in the range 60 to 600s, before cooling again. Steps (iv) to (vi) particularly effect a preliminary ageing to prepare the sheet for a subsequent paint-bake as an automotive body part.

Jan Bottema

Papers

Recent development in aluminium alloys for the automotive industry

Improvement in Bake Hardening Response of Al-Si-Mg Alloys

Recent Developments in AA6016 Aluminium Type Body Sheet Product

The Effect of Small Particles on Annealed Grain Size and Texture of Al-Mg-Si Alloys

Method for the manufacture of aluminium alloy sheet