The reason was that a mass of oxidation inclusion in steel which induced low ductility, toughness and fatigue intensity, and finally had bad machininged capability.

Decreasing welding thermal input will decrease the oxygen content and the number and size of oxide inclusions, and it improves the toughness of weld metal.

The purification effect of Al-Si melt by composite refining technique was studied, the main existing form and its interaction of inclusion and gas in Al-Si melt were introduced.