Sheet ingot materials for ultra-thin automotive heat-exchangers

Modern cars contain up to ten different heat-exchangers, sometimes more. Aluminium brazed products are clearly dominant in the heat-exchanger industry and the production chain start by casting of sheet ingots, followed by homogenisation, clad application, pre-heating, hot rolling, cold rolling, intermediate or final heat treatments and slitting. There is an increasing demand for improved aluminium products strongly linked to the global vehicle development and production. New designs are more compact, even lighter and more efficient to further reduce fuel consumption and emissions. At the same time, the operating temperature of the heat-exchangers in newer motors is increasing and puts additional demands on the material strength. Weight reductions through down-gauging of the sheet thickness have been a trend over years. However, further down-gauging is now a major challenge limited by the material as-cast microstructure and properties. This project has addressed the development of sheet ingot materials (3xxx alloys) that would allow further down-gauging during down-stream processing and even lighter heat-exchangers. Microstructure control and the mastering of particle sizes is crucial. In addition, the materials should have low-scrap rates during casting and excellent material properties. Efforts have been made to establish a coupling between the between the alloy composition, the solidification microstructure and the cracking sensitivity both experimentally using numerical models and in casting trials. The effect of process parameters, cooling conditions as well as variations in the casting technology on the cracking sensitivity was assessed. A first evaluation was done using process modelling before selected variations were tested in industrial casting trials. The efforts have resulted in process and alloy improvements giving a reduced scrap-rate during casting. Formation of large particles during solidification have been studied using microstructure models and experiments. An increased understanding of mechanisms have led to a better control of the particle sizes in the material.

Competence on casting of difficult-to-cast alloys with stringent requirements on ingot quality. Improved products and processes. New experimental and numerical toolboxes.

n increasing demand for new heat exchanger aluminium alloys is strongly linked to the global vehicle development and production. Designs must be more compact, even lighter and more efficient to further reduce fuel consumption and emissions. At the same time, the operation temperature of the heat-exchangers in newer motors is increasing, which puts additional demands on the material strength. Weight reductions through down-gauging of the sheet thickness have been a trend over years. However, further down-gauging has now become a major challenge limited by the material quality of the sheet ingots. This project aims at development and production of new Al-Mn series sheet ingot materials for with a microstructure that allows further down-gauging of the sheets. In addition, the new alloys shall not compromise material strength and corrosion properties and be highly castable. The project goal shall be a achieved by alloy development through control of raw material qualities and alloy compositions. A key success factor is microstructure control and the mastering of inclusion and particle sizes. The alloy development will be extended by coupling microstructure and cracking tendency during casting as well as improvement of casting equipment and procedures for a cost-competitive production.