The use of aluminium alloys for automotive heat exchangers has increased considerably in the last 15-20 years and, in parallel, new alloys have been developed to meet the increased demand for strength and improved corrosion resistance. A non-heat treatable Al-Mn alloy, X800, has been developed by Alcan to significantly increase the corrosion resistance of radiator tubes when subjected to typical service environments. The alloy development employed considerable microstructural understanding to provide heat exchanger manufacturers with an improved product that readily attained enhanced performance during any brazing cycle.A similar philosophy has been adopted to address the issue of increased mechanical performance, higher intrinsic sheet strength, both during and after brazing, provides the opportunity for sheet downgauging and thus lightweighting of components. These are key requirements in an industry sensitive to the need for fuel economy and sound environmental practices whilst maintaining or improving component performance. It is only by the detailed understanding of those microstructural features that control sheet properties that new alloys can be successfully developed to meet these stringent demands.This paper will discuss the options for enhancing the mechanical performance of brazing sheet and detail the development of a second generation for X800, Alcan's new X900 brazing sheet core alloy. Reference will be made to the control of microstructural features that are important to this new alloy and that create the significantly increased strength without detriment to the long-life corrosion behaviour of the parent alloy.