The weight of automobiles has been continuously increasing during the years with improving performance, comfort and safety features. At the same time the importance of environmental issues are of great concern because an increase in weight of the automobiles directly leads to an increase in the emission of CO2 gas. Due to the global emissions-driven push for weight reduction in cars, there are growing opportunities for lightweight aluminium alloy automotive body panel materials to compete effectively against traditional steel body panels. As a result, there has been significant growth in the use of aluminium alloy body panels, particularly in
Europe, where aluminium alloy panels are now used in more than 2.5 million vehicles each year. According to the European Aluminium Association, the market share for aluminium alloy usage in car bonnets is about 18% in Europe, 8% in America and 3% in Asia. These percentages decrease significantly with increasing part complexity [1, 2].
These applications require alloys having properties like a high strength to weight ratio, dent resistance, corrosion resistance and good formability . Apart from material and manufacturing cost, the poorer formability of aluminium alloys compared to that of steels is one of the most important reasons for the relatively low market penetration of aluminium alloys for automotive body sheet applications . Various 6xxx series wrought aluminium alloys have been developed for the above-mentioned requirements. The need for producing high quality 6xxx series alloy sheets with good formability and low manufacturing cost is inevitably related to precision alloy design, cold rolling and heat treatment techniques .
Currently, there are many issues with the formability, surface appearance and the corrosion properties of 6xxx series wrought aluminium alloys. These alloys are known to suffer from a phenomenon called ridging or roping. These are
Bibliography:  T. Sakurai, Kobelco Technology Review, 28 (2008) 22-28.  http://www.alueurope.eu/pdf/Aluminium_in_cars_Sept2008.pdf European Aluminium Association (2008).  Prantik Mukhopadhyay, ISRN Metallurgy, 165082 (2012) 1-15.  G. Davies, Materials for Automobile Bodies, Elsevier, (2003) 61-90 and 146-155.  O. Engler, C. Schafer, H. J. Brinkman, Acta Materialia, 60 (2012) 5217-5232.  M. J. Starink, L.F. Cao, P.A. Rometsch, Acta Materialia, 60 (2012) 4194-4207.  R. K. Gupta, N. L. Sukiman, K. M. Fleming, M. A. Gibson, N. Birbilis, ECS Electrochemistry Letters, 1(1) (2012) C1-C3.