Tribological behavior of Al–6.5%, –12%, –18.5% Si alloys during machining using CVD diamond and DLC coated tools

• H-DLC coatings improved tool life during drilling of low Si grade of hypo and eutectic Al–Si alloys.
• A tool failure criterion based on rate of torque increase was established.
• Tool failure of Al-(6.5% - 12.0%)-Si alloys was due to Al adhesion.
• H-DLC coatings improved tool life during drilling of grade Al-(6.5% - 12.0%)-Si alloys.
• CVD diamond prevented flank wear during drilling of Al-18.5% Si alloys.

Tribological behavior of cast Al–Si alloys was studied by considering samples from hypo-eutectic (Al–6.5% Si), eutectic (Al–12% Si) and hyper-eutectic (Al–18.5% Si) compositions that were subjected to dry drilling experiments. Tool materials tested consisted of hydrogenated diamond-like carbon (H-DLC), CVD diamond coated and uncoated WC–Co drills. Tool failure mechanisms were identified and correlated with the drilling torques. The drilling torque vs. number of holes curves typically exhibited three stages, each identified with a characteristic slope (m). A failure criterion was established, such that when m ≥ 1.0 × 10− 2 N m the onset of tool failure in dry drilling of Al–Si alloys could be predicted. For hypo-eutectic and eutectic Al–Si alloys drilled using uncoated WC–Co the failure criterion was satisfied rapidly (< 70 holes) and extensive aluminum adhesion to the drill occurred. The use of H-DLC and CVD diamond coated drills reduced aluminum adhesion and built-up edge formation, and maintained m ≤ 1.0 × 10− 2 N m throughout the drilling tests range. Drilling of hyper-eutectic Al–Si alloys with the H-DLC coated drills led to shortened tool lives characterized by flank wear as the primary Si particles abraded the coating and increased the friction. CVD diamond coated drills produced low tool wear and maintained low steady state m values. It was concluded that during dry drilling of Al–Si alloys, where aluminum adhesion was a performance limiting factor, H-DLC coatings could replace CVD diamond tools.