| Due to the need of lightweight, energy saving and environmental protection, aluminum alloys are more widely used in various industries. But the low strength limits applications. Therefore, three kinds of powder mixtures, CuZn-WC, Ni-WC, and Ni-MoFe as pre-coated materials in this paper were prepared to carry out argon arc cladded experiments by TIG welding machine on the pure aluminum substrate to improve the wear resistance of the aluminum surface. The microstructures and properties of surface layers were studied by changing processing parameters and powder mixture ratios.The study on microstructures and properties of surface layers obtained by argon arc cladded CuZn-WC on pure aluminum substrate indicated that the phases in surface layers were α-Al solid solution, a small amount of Al4 W compounds and agglomerates of CuZn alloy with WC when WC contents were less than 60 wt.% in the pre-coated powders, while the phases of surface layers included α-Al solid solution, a large amount of lath-shaped or lump Al4 W compounds and a small amount of agglomerates of CuZn alloy with WC when WC contents were equal to or more than 60 wt.% in the pre-coated powders. With the increase of WC contents in the pre-coated powders, the amount and size of Al4 W compounds increased and the microhardness of surface layers also increased, which was up to its maximum of about 4.5 times higher of the pure aluminum substrate and the corresponding wear resistance was about twice as high as the pure aluminum substrate.The study on microstructures and properties of surface layers formed by the argon arc cladded Ni-WC on the pure aluminum substrate at different cladding currents showed that the surface layers with good microstructures and properties were obtained when the cladding current was 160 A. The research on the mass ratio chang of Ni to WC in pre-coated powders at 160 A indicated that when Ni contents were equal to or more than 90 wt.%, the surface layers would contain a large amount of Al3Ni2 and Al3 Ni compounds. The main morphology of which is equiaxed Al3Ni2 grains surrounded by Al3 Ni compounds. The average microhardness and the wear resistance were 11 and 3 times higher than aluminum substrate. When Ni contents were 30 wt.%-80 wt.%, the dendrite Al3 Ni and irregular shape Al12 W compounds distributed on α-Al solid solution and Al3 Ni and α-Al eutectic microstructures appeared on the lower part of the surface layers. The average microhardness of surface layers was 4 times higher than aluminum substrate and the wear resistance was one time higher than aluminum substrate. When Ni contents were 10 wt.%-20 wt.%, the phases in surface layers were composed of α-Al solid solution, lath-shaped or lump structure Al12 W and a small amount of Al3 Ni compounds. The thickness of surface layers became thinner for the lack of fusion, which leaded to denser compounds in the surface layers. The average microhardness was about 6 times higher than aluminum substrate and the wear resistance was one time higher than aluminum substrate. When the pre-coated powders are 100 wt.% WC, the Al4 W compound was found in the surface layer as reinforced phase. In that case, the surface layer was lack of fusion on the aluminum substrate and the microhardness and wear resistance were not apparently improved.The study on microstructures and properties of the surface layers formed by argon arc cladded Mo Fe on pure aluminum substrate under different current showed that the phases in surface layers when the current was between 100A-120 A was consisted of white block Al2.72Fe0.28 Mo, gray-white Al5Fe2 and white α-Al solid solution. The average microhardness of surface layers was 25 times higher than the aluminum substrate and the wear resistance is three times higher than the substrate. The phases in surface layers at 140A-160 A were made up of gray-white strip, block or irregular shape Al4 Mo, dark-grey lath-shaped Al3 Fe and α-Al solid solution. The average microhardness and the wear resistance of surface layers were 10 or 2.5 times higher than the aluminum substrate correspondingly. When current was up to 180A-200 A, the phases in surface layers were composed of gray-white strip or block Al5 Mo, dark-gray ten angle star Al3 Fe and α-Al solid solution, the average microhardness increased a little.When the current was 160 A and the pre-coated powders were combined of 80 wt.% Ni-20 wt.% MoFe or 60 wt.% Ni-40 wt.% MoFe, the phases in surface layers consisted of black-blue granular or strip Al3 Ni, rust-red strip Al3 Fe, soil-yellow strip or irregular shape Al5 Mo compounds and α-Al solid solution. While only MoFe powders were pre-coated on the substrate, the phases of strip Al3 Fe, block-strip or irregular shape of Al4 Mo compounds and α-Al solid solution were found in the surface layers. Among all these specimens, small size and relatively sparse compounds made the average microhardness of surface layers as high as 230-290 HV, which was about 8-10 times higher than the aluminum substrate. The wear resistances were increased 3.5 times. Only Ni pre-coated powders gave rise to surface layers in which phases were composed of black Al3 Ni and gray equiaxed grains of Al3Ni2, a small amount of Ni granules and α-Al solid solution. These compounds densely distributed in the surface layer. When the pre-coated powders was composed of 40 wt.% Ni-60 wt.% MoFe or 20 wt.% Ni-80 wt.% MoFe, the phases in the surface layers were made up with white Al2.72Fe0.28 Mo compounds with regular shape, soil-yellow Al5 Mo compounds with irregular shape, rust-red strip Al3 Fe, a small amount of dark-blue Al3 Ni compounds and α-Al solid solution. These large and dense compounds in the surface layers made the average microhardness reached up to 330-470 HV, which was about 11-17 times higher than the aluminum substrate. The wear resistance was improved 3.5 times.As presented above, the most dense structure with many kinds of large size compounds were found in the surface layer which had good metallurgical bonding to the aluminum substrate when the pre-coated powders were composed of 20 wt.% Ni-80 wt.% MoFe. The average microhardness and wear resistance were respectively up to 470 HV and 3 times higher than aluminum substrate. The excellent microstructures and properties were obtained in this surface layer. |
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