Effects of Sn and Bi addition on cutting performance of Al-Mg-Si alloy were investigated by comparing the chipping shape

surface roughness and tangle cutter condition in process of cutting of three kinds of Al-Mg-Si-（Sn

Bi） alloys. The existing forms of Sn and Bi in the Al-Mg-Si alloys were observed to understand their ralein cutting performance of alloy by XRD （X-ray diffraction） and SEM （scanning electron microscope）. The results reveal that formed Mg2Sn

Mg3Bi or Sn phase in Al-Mg-Si alloy can result in the brittle crack of chip as a result of softening during high speed cutting process

while they can form cavity or crack to result in chip fracture due to deformed rate different from matrix during low velocity cutting process

improving the cutting performance of the alloy. In addition

cutting performance of Al-Mg-Si alloy with mixed Sn and Bi addition is superior to that of ones with only Sn or Bi addition.