Tribological investigation on friction and wear behaviour of coatings for hot sheet metal forming

Since hot sheet metal forming has become a key technology to produce high strength steel parts for modern automotive construction, detailed knowledge of tribological behaviour of coated steel blanks at elevated temperatures is necessary. Therefore, hot dip aluminium–silicium and electro-plated zinc alloy coatings for hot forming applications have been evaluated according to their friction and wear behaviour. The coefficient of friction was revealed in hot strip drawing experiments. Moreover, mass loss of the workpiece has been measured to characterize the amount of wear. According to the different constitution of the Al–Si coating in comparison to the electro-plated Zn–Ni after heat treatment, the zinc alloy coating showed higher mass loss but lower coefficient of friction. Additionally, wear characteristics have been evaluated in hot forming tests. Herein, parts formed of Al–Si coated blanks showed as well a lower mass loss but more aggressive wear behaviour by means of adhesive wear to the die, resulting in metallic build-up onto the die radius. In contrast, the workpiece related mass loss was higher for Zn–Ni but considerable metallic build-up layers onto the die did not occur. This may be advantageous in production lines hence maintenance and reconditioning frequency of the forming tools could be reduced.