Wear effects on coated tools during the alternating forming of case-hardening steel and aluminium wrought alloy

A major factor for a high economic profitability in industrial bulk metal forming is the
material-specific wear of the forming tools, which has a significant influence on process
reproducibility. Particularly in Tailored Forming, in which hybrid material combinations are
processed, narrow and sensitive process windows are characteristic. During impact extrusion of
joined hybrid semi-finished workpieces made of steel and aluminium, the extrusion shoulder is
subjected to combined wear phenomena. Adhesion and abrasion are superimposed, whose
interactions lead to process fluctuations and premature failures in the absence of sufficient wear
resistance. To investigate the yet unknown combination of the interactions, upsetting tests are
carried out in cycles of 100, in which steel (AISI 5120H) and aluminium (AA-6082) are hotformed
alternately. In addition to tempered and nitrided tools, duplex coatings such as chromium
nitride and titanium aluminium nitride are used to evaluate the potential of reducing the occurring
wear phenomena through surface engineering methods. After the first cycles, the tools exhibit
needle-shaped adhesion marks consisting of aluminium, which were subsequently transferred
primarily to the steel workpieces during upsetting. Since adhesion is more present at the tool edge,
an increased adhesive tendency with longer flow paths is observed. Due to the improved
tribological conditions, duplex coatings minimise the wear volume on the tool and potentially on
the formed workpiece with short contact times.