Influences of RE element on microstructure of 7075aluminum alloy were investigated by OM（optical microscope）

EDS（energy dispersive spectrometer） and SEM（scanning electron microscope）.The results verify that when RE addition is in range of 0.2%～ 0.5%

with increasing in RE addition

as-cast grain size in the alloy exhibits firstly decreased and then increased

showing desirable refinement effects.With 0.3% RE addition

minimum grain size in the alloy can be observed

and desirable comprehensive mechanical properties can be obtained

however

with 0.5% RE addition

grain size becomes coarse and acicular enrichment phase appears

resulting in the deterioration of comprehensive mechanical properties of 7075aluminum alloy.