STRAUSS - Superior Temperature Resistant Aluminium Steering Shafts

When coldforging aluminium components at room temperature, it is very important to ensure that the blanks are as ductile as possible. By adapting alloy content, process parameters and heat treatment/soft glowing, it shall be ensured that the blanks have a uniform and lowest hardness possible before the forming takes place. In the first part of the project, experiences and data from manufacturing have been collected and used as the basis for a large number of experiments to reduce the hardness of the blanks before pressing. In addition, expertise from past research at Sintef, together with literature searches and other sources, has been used in the preparation of the test program for optimization of the material. Heat treatment/softening of a high-temperature stable material, which is designed to precisely retain strength and hardness at high temperatures over a long period of time, has proved to be no easy task. Studies of the microstructure and the dispersoids and phases found in the material before and after soft glowing has been examined under a microscope, and theoretical calculations have been carried out to determine, if possible, the theoretically lowest possible limit of hardness and electrical conductivity. The experiments so far have shown that there actually is a lower limit to how soft the material can be, regardless of the method used. The aim of the project is to achieve a low and stable hardness and thus increased formability without compromising strength, fatigue and corrosion properties. As expected, the results from laboratory and serial production equipment are somewhat different, and the experiments have revealed that there are individual variations between the thousands of blanks treated simultaneously, depending on their position in the heat treatment furnaces, and depending on the program for controlling the heat treatment equipment. Changes have therefore already been made to serial production in how the furnaces are used to offset the differences. Laboratory experiments has revealed that in addition to variations from part to part, there are also variations within the same blank, and that it is influenced by the heat treatment process. The cold-shaped products undergo two additional heat treatment processes before they are ready to be delivered to the customer, namely solution heat treatment (SHT) and artificial ageing (AA). The effect of intermediate storage times between forming - SHT - AA has been tested, along with preheating the blanks before pressing and reheating the products for a time after hardening. All these experiments have provided knowledge that will be followed up in the coming year. New alloys with altered content of alloying elements have been molded and extruded, with the view of reducing deformation hardening by pressing, as well as contributing to increased mechanical strength, temperature stability and corrosion resistance. The physical and metallurgical examinations of the alloys are running. The results so far have given us some surprises, so we are looking for an exciting 2022.

In a range of car models, the steering shaft is close to high-temperature components (engine, exhaust), and strict requirements with respect to temperature toughness are set by the car manufacturers to prevent product failure. Presently, no mass-produced aluminium solution can meet the specifications. Hence, even if aluminium is preferred based on design possibilities and weight-saving, the car manufacturers are still prescribed to choose a solution in steel in applications where the temperature load is high. The proposed innovation will be developed to ensure an economic, high-quality and high-productivity manufacturing of temperature resistant steering components for the automotive industry. This will give car manufacturers the possibility to further reduce the weight of the vehicle and consequently improve the vehicle fuel consumption and lower the CO2 emissions. The innovation will allow Steertec to enhance their position in the automotive market, with a series of steering shafts and other components that can respond to the current as well as future challenging product specifications. In the fierce international market, the components represent a light-weight alternative not offered by competitors, and it will give Steertec a competitive advantage. The realization of the innovation requires intensive research effort from the industrial partners Steertec Raufoss AS (STR) and Thune Produkter Raufoss AS (TPR). The complementary research effort from the research partners (SINTEF Industry and SINTEF Manufacturing) is essential to obtain the envisaged results. The research partners will contribute with competence, advanced characterization equipment, forming equipment and corrosion testing.