Effects of the drill flute number on drilling of a casted AZ91 magnesium alloy

This experimental study aims to reveal the effect of the drill flute number on the thrust force, tool wear, tool life, chip morphology, surface hardness and microstructure in the drilling of a cast AZ91 magnesium alloy. The results showed that the cutting flute number and cutting parameters have an important effect on thrust force, tool life, wear, chip morphology, microstructure, and drilled hole hardness. When the 2-flute drill was used, less thrust force was generated during the drilling. On the other hand, less tool wear occurred with the 3-flute drill. In scanning electron microscopy (SEM) microstructural analyses, grain refinement was observed in the microstructure of the borehole surface although grain growth was also observed due to a rise in temperature. In addition, the microhardness of the borehole surface decreased as the number of holes increased, and the 2-flute drill bit provided holes with higher stiffness than the 3-flute drill bit.