AZ31 magnesium alloy was subjected to surface solid thermal diffusion treatment with La

2

O

3

and pure Zn powder at 390 ℃ for 4 h

and the mass fraction of La

2

O

3

in the diffusion agent is 0

0.2%

0.4% and 0.6%

respectively. The evolution of the infiltrated layer microstructure of Mg alloy surface with adding different mass fractions La

2

O

3

was analyzed. The hardness of the diffusion layer and the erosion corrosion wear performance in 3.5% NaCl solution and quartz sand were tested. The results show that without infiltration agent addition

the diffusion capacity of Zn atoms is insufficient and absence of infiltration layer can be observed. With 0.2% infiltration agent

the diffusion capacity of Zn atoms is enhanced

and different Mg-Zn compounds(Mg

0.97

Zn

0.03

+β-Mg

17

Al

12

+α-Mg+MgZn+Mg

2

Zn

3

+MgZn

2

) appear in the diffusion layer

where La

2

O

3

plays the role as a catalyst during the diffusion process. With the increase of La

2

O

3

in the infiltrant

when the content of La

2

O

3

in the infiltrant exceeds 0.4%

the matrix of the AZ31 magnesium alloy disappears

and the number of phases in the layer is absent change. With increasing in La

2

O

3

the microstructure is coarsened increasingly

and the change in structure results in changes in hardness and erosion corrosion performance. The hardness is increased with the increase of La

2

O

3

in the osmotic agent

and the scouring corrosion wear performance presents desirable when the La

2

O

3

content is 0.2%.