Surface treatment of aluminium automotive sheet: Mythology and technology

Abstract

The use of aluminium automotive sheet to save weight, fuel and carbon emissions is increasing as EU OEMS strive to reach progressively tougher targets and from the need to avoid fleet average penalty payments. Surface finishing of structural sheet for alloys like AA5754 generally involves cleaning and pretreatment followed by roll coating with a lubricant. For alloys supplied for body panels like AA6016 and its variants, surface treatments can include a mechanical texturing treatment followed by cleaning and pretreatment with a stabilising treatment and then spray coating with a dry film lubricant. Surface finishing capacity in the EU is now available on six finishing lines with an estimated total capacity of about 350 kt/year. This is just about in balance with present demand, but the capacity of the existing lines will soon be exceeded by the rapidly increasing demand. Further finishing lines will be required to keep pace with the increasing demand. There is a difficult balance to achieve between cost and finishing process complexity and the demanding requirements of formability, adhesive bond durability and surface appearance specified by the automotive companies in the EU. It is important to understand the need and value of each of the finishing treatments considered to be essential for automotive sheet supply in the EU compared to the less stringent requirements applied in North America and Japan. The complex microstructural and technological issues surrounding surface finishing and sheet performance will be analysed and discussed in detail and opportunities identified.

Design and ageing of adhesives for structural adhesive bonding – A review

“…48 To improve the stability of the surface and achieve direct chemical bonding between the oxide and the adhesive, various silane based treatments have been developed. 50–52 Organosilane primer process, based on an aqueous solution of γ-glycidoxypropyl trimethoxysilane (γ-GPS), is widely used as an oxide primer. Parameters such as temperature of cure, ageing time and concentration of the aqueous solution influence the performance of the primer.…”

“…53 Aluminium, titanium and steel substrates all have their performance enhanced by treatment with silane primers. 42,50 The effectiveness of the pre-treatment depends on whether the aluminium is an alloy or an aluminium clad sheet material. In order to improve the mechanical properties of aluminium and lithium, copper and magnesium can be incorporated in the alloy which will influence the nature of the oxide grown and its sensitivity to moisture.…”

Multifunctional Aluminum Pre-treatments from End-Functionalized Phosphonic Acid Self-Assembled Monolayers

“…There have been studies to modify the lubricant composition to improve lubricant spreading on the surface, , with some successful results in reducing friction and wear. The surface energy of a metal substrate, on the other hand, can be modified by physical or chemical surface treatments including, for instance, plasma treatment, which lacks industrial scalability; etching procedures using inorganic acids, which can be used for short-term wettability improvement; and treatment with surfactants bearing appropriate chemical functionalities for surface binding. − Moreover, improved bonding performance and durability in the joining step, as well as corrosion inhibition, are typically achieved by employing Ti/Zr-based or silica-based pre-treatments. − …”