Effect Of Various Sliding Velocities And Substrate Hardness On Wear Resistance Of Hot Dip Aluminized Steel

Fe-Al intermetallic compounds have been widely prepared on the surface of steel using a hot dip aluminizing?HDA?surface modification method to expand and improve the application of steel,due to its excellent high temperature oxidation resistance and corrosion resistance as well as low density,high specific strength,etc.Until now,there are few studies on the wear properties of hot dip aluminized steels,and studies reported on the wear behavior were conducted at high temperatures and low velocities.Therefore,it is of great practical significance to study the wear properties of hot dip aluminized steel and explore its wear mechanism at room temperature and high speed conditions.In this paper,intermetallic compounds coating was prepared on 45 steel matrix material under different dip technologies and diffusion annealing conditions.The dry sliding wear tests were performed for a hot dip aluminized steel prepared by diffusion annealing at 1050°C for 4.5 h in various substrate hardness and sliding parameters on a MPX-2000 frictional wear tester to study the wear behavior.The composition,microstruture and performance of the coating and the phase,morphology,composition and property of worn surface and subsurface were separately studied and characterized by SEM,EDS,XRD,Raman spectrometer,microhardness tester and electrochemical workstation to explore the wear mechanism of hot dip aluminized steels.Results showed that the coatings at different dip temperature and time were all composed of Fe₂Al₅ alloy layer and pure aluminum layer.The morphology and thickness of coatings were affected by the dip temperature and time.The coating dipped for 5 min at 750°C was tight,combined well with the matrix and had evenly distributed serrations.All coatings at the diffusion annealing temperature of 850°C or less contained Fe₂Al₅ brittle phase,which showed a zigzag bond with the matrix.At1050°C,coatings consisted mainly of the ductile phase FeAl and Fe₃Al,and showed good metallurgical bonding with the matrix with a straight interface.As the diffusion time increased,the thickness of coatings became thicker and the proportion of Fe₃Al layers increased.The wear study showed that the wear rate decreased significantly with the increase of the sliding speed between 0.75-1.5 m/s and remained almost unchanged at1.5-2.68 m/s.When the sliding speed increased to 4 m/s,the wear rate slightly increased.And the increasing rate was bigger when the substrate hardness and load increased.It was found that the tribo-layer was generated on the worn surface of hot dip aluminized steel at different sliding speeds.Different sliding conditions led to different characteristics and properties of the tribo-layer,which caused changes in the wear mechanism of the hot dip aluminized steel and determined the wear resistance of the hot dip aluminized steel.The substrate hardness was inversely proportional to the thermal stability of the structure and affected the stability of the tribo-layer.The degree of influence on the wear rate was related to the load,and it was not obvious under a low load.With increasing the substrate hardness at 50 N,the wear rate increased.At 0.75m/s,the tribo-layer containing less oxides was metal-predominant.It hardly protected the matrix material due to its discontinuity?small thickness and low hardness.In this case,main wear mechanisms were adhesive wear and abrasive wear.At 1.5 m/s,35-40 HRC and 2.68-4 m/s,the tribo-layer containing more oxides was ceramic-predominant.It played an excellent role on protecting the matrix material due to its continuity,big thickness and high hardness.In this case,the wear mechanism was mild oxidation wear.At 1.5 m/s,45 HRC,the tribo-layer was peeled off and the coating underwent severe brittle fracture due to the poor thermal stability of the substrate.In this case,protective funtion of tribo-layer was reduced due to the formation of a double-layer structure and the wear meachanism turned out to be brittle fracture and oxidation wear.