Research Of TiAl₃ Reinforced Aluminum Matrix Composite Coating By Laser Surface Alloying

Based on the thermodynamics of chemical reaction between Ti and Al under the high temperature, the TiAl3 intermetallic reinforcing layer is prepared on surface of ZL117 aluminum alloy by laser surface alloying technology using 6kW transverse flow CO2 laser device. The microstructure, distribution of Vickers hardness and high temperature oxidation resistance of the alloy reinforcing layer is analyzed by using X-ray diffraction (XRD), energy dispersive spectrum (EDS), X-ray photoelectron spectroscopy (XPS), optical microscope (OM), scanning electron microscopy (SEM), Vickers hardness gage and muffle furnace. To provide theoretical basis for repairing the damaged surface of ZL117 aluminum piston alloy by using laser surface alloying technology, the influence of the alloy layer microstructure and high temperature oxidation resistance of the alloy reinforcing layer by different the laser parameters is mainly analyzed.X-ray diffraction phase analysis result shows that the alloy reinforcing layer is composed of TiAl3, α-Al and a bit of Si. Without the peak of Titanium, means that the TiAl3 is completely reacted by Titanium and Aluminum. It has displayed from the EDS of the alloy reinforcing layer’s middle part, the atomic ratio of Ti and Al is closed to 1:3 in the light gray net structure, affirmed TiAl3.The atomic ratio of Al and Si is closed to 9:1 in the dark gray net structure, affirmed eutectic structure of Al and Si. XPS analysis indicates that Ti is existed as TiAl3 in the alloy reinforce coating. The binding energy in TiAI3 is 460 ev and Al is existed as TiAl3, Al2O3 and Al form, and their binding energy are 73.60 ev,75.82 ev and 72.90 ev.When the laser power P=4.3 kW, the scanning rate v=5.0 mm·s-1, OM phase and SEM indicate that the Ti powder of alloy reinforcing layer present good metallurgical bonding with the substrate. The porosity and crack defects have not shown in bonding interface. In the top of the alloy reinforcing layer gets net structure, and dendritic structure and slender needle nascent structure can be seen in the bond zo ne.Micro hardness distribution curves show that at the same scan rate, the content of TiAl3 in the alloy reinforcing layer increases along with the laser power, and a network structure is formed. The effect of enhancement is proportional to the content of TiAl3 in the alloy reinforcing layer. The micro hard ness value of TiAl3/Al alloy reinforcing layer is highest 340HV0.2,5.31 times of the substrate.High temperature oxidation text shows that after 80 hours constant temperature of 600, the alloy reinforcing layer surface gets Al2O3 and TiO2, ZL117 alloy surface gets Al2O3 and a bit of SiO2. At the same condition of the high temperature oxidation, the layer has a small weight gain and oxidation rate, so a better property against oxidation under high temperature is shown which the relatively antioxidative value is up to 2.64.