Microstructural evaluation and corrosion properties of aluminium matrix surface composite adding Al-based amorphous fabricated by friction stir processing

A novel aluminium matrix surface composite adding Al84.2Ni10La2.1 amorphous, which the layer depth was 5 mm, was fabricated by friction stir processing. The surface composite region shows obvious sandwich structure. The average hardness of the surface composite is about HV97, higher than the base metal is about HV80. The maximum tensile strength of the processed aluminium plate with the surface composite is 410 MPa. The surface composite was mainly composed of phases α-Al, Mg2Al3, MnAl6 and La3Al11. The surface composite added the amorphous strip had the lower icorr, corrosion current density, and the higher passivation current than the surface composite not added amorphous strip. And there is obvious passivation zone for the surface composite. However, a large number of ultrafine grained which was composed of the α-Al and α-Al amorphous structures can be observed in the surface composite. And the grain size range of them is 90-400 nm. It is conceivable that the existence of these ultrafine grained structures and change of crystal plane would contribute greatly to improve the mechanical properties and corrosion resistance of the aluminium matrix surface composite.