The erosion of contact material plays a crucial role in the reliability and life of low-voltage circuit breaker. Therefore

it is important to develop an erosion model. In this paper

the contact erosion model including both vaporization and sputter erosion is established to determine the mass loss under direct current air arc. A two-dimensional magnetic hydrodynamics（MHD） for molten pool is combined with the solidification and melting model to calculate the melting phase change process. Moreover

the vaporization erosion model and sputter erosion model are established on the basis of molten pool model. The vaporization erosion model is based on the Langmuir formula and the gas dynamics. The relations between vaporization flux and surface temperature of molten pool is analyzed. The sputter erosion model is built based on statistical methods and the mass loss of sputter erosion is obtained. In addition

the influences of material property

current

the size and shape of contact on the contact erosion are studied so as to obtain an effective way to reduce contact erosion. The results show that the evaporation erosion is dominated when the current is lower than 20 A. The sputter erosion plays the major role when the current is higher than 200 A. On the premise of ensuring that the contact size is greater than the size of the molten pool

reducing the radius of cylindrical contact can reduce erosion

but the effect is minimal. Under the same conditions

the erosion mass of the domed contact is the greatest. The erosion mass of the cone-like contact comes next and the erosion mass of the cylindrical contact is the least.