Experimental study on aluminum bronze coating fabricated by electro-spark deposition with subsequent ultrasonic surface rolling

Aluminum bronze coatings were prepared on the as-cast substrate of the same material by electro-spark deposition (ESD), and the coatings were treated by ultrasonic surface rolling (USR). The effects of USR on the microstructural, mechanical, and tribological properties of the ESD coatings were investigated. The microstructure, phase composition, nanoindentation, microhardness, surface residual stress, and tribological properties of the coatings were experimentally determined and characterized in detail. The USR treatment with different static pressures (1.0 MPa, 2.5 MPa, 4.0 MPa) was employed to reveal the mechanism of microstructure evolution and surface modification. The results showed that the original columnar crystal structure of the coatings treated by USR was deflected, elongated, and even broken, resulting in the grain refinement of the coatings. The hole defects were healed after USR2.5 treatment. The phase composition of the coatings changed from β′ (Cu3Al) phase to α (Cu) and κ (Fe3Al) phase because of the heat released at USR. The nanohardness, static creep resistance, and microhardness of the ESD coatings were effectively promoted by USR. The nano-hardness of the ESD coating after USR4.0 treatment (4.4 GPa) was 1.38 times and 2.2 times that of the ESD coating and the as-cast alloy respectively, and the creep displacement (5.193 nm) was 27.2% and 18.5% that of the ESD coating and the as-cast alloy respectively. The residual tensile stress of the ESD coatings was eliminated after USR treatment and converted into the residual compressive stress. The surface residual stress of the ESD coating after USR2.5 was −337.16 MPa. After USR2.5 treatment, the wear loss of ESD coating reduced by about 1/2, which was attributed to the healing of hole defects, residual compressive stress, and the increase of the hardness.