The Microstructures And Properties Of Surfacing Layers Hardened By Nitrogen Arc Processing On ZL101Aluminum Alloy

Using TIG welding, AlN/Al-Si composite coating was prepared on the surface ofZL101by nitrogen arc, with high purity nitrogen as protective and reactive gas.Scanning electron microscopy (SEM) was used to observe the microstructure ofsurface layer; X-ray diffraction (XRD) was used to test the phase composition insurface layer, and the energy spectrum analyzer (EDS) was used to test the elementsof the nitride layer.The research results indicated that the surface layer hardened by nitrogen arc onZL101mainly consisted of the AlN dendrites and Al-Si eutectic compounds. Thechange of the arc current or the proportion of arc atmosphere would impact themicrostructure and properties of the surface layer. With the increasing of current orthe ratio of nitrogen in the arc atmosphere, the heat input and the nitrogen diffusinginto the pool increased, which resulted in the generation of AlN increases, and thedendrites became intensive. While the current or the ratio of nitrogen in arcatmosphere continued to increase, the content of AlN generation reduced but thedendrites increased, the microstructure changed. This is because the relative dilutionrate of matrix became larger. It is revealed that the content of AlN in surface layer andthe microstructure of AlN directly affected the mechanical properties of the materialsurface, and the increase of current or the amount of nitrogen properly would increasethe hardness and wear resistance of surface layer. This paper also studied thedifference of DC nitriding and AC nitriding. The microstructure of surfacing layers byAC nitriding was layer structure, which was much more uniform, but the hardness andwear resistance was worse than DC surface layer. With the current increasing, thenitrogen layers became thicker, and the hardness and wear resistance also increased.In this paper, the test prepared the powder of Fe and Ti, and then processed thesurface of ZL101by nitrogen arc, which included AlN phase, Al0.7Fe3Si0.3phaseandα-Al phase. Two kinds of typical microstructure were observed in the different currentsituation, in the small current conditions, dendrites AlN, needle Al0.7Fe3Si0.3，α-Al wasobserved; while in the large current condition, the microstructure was laminated AlN, Chinese characters shape or petal shape Al0.7Fe3Si0.3，α-Al. With the depth of surfacelayer increasing, the amount of N diffusing into the pool became less, and themicrostructure produced was also different. With the currents increasing, the thicknessof surface zone became thicken and then thin, the content of AlN dendrites firstincreased and then decreased, the hardness and wear resistance also hadcorresponding change.Research showed that, when the current was120A and nitrogen content occupied40percent in the arc atmosphere, the combination properties of surface layer was thebest.