Study On Microstructure Evolution And Mechanical Properties Of Al-Steel Plain Bearing Using Arc Additive Manufacturing

With the increasing demand of high travel speed and load carrying capacity of motorengine,Al-steel bimetallic plain bearing has been widely used in passenger vehicles because of its advantages of high strength,good thermal conductivity and low price.In order to further improve the bonding strength between aluminum alloy layer and the steel back,and to expand the new manufacturing technology of aluminum alloy layer coating on thick wall steel back.In this paper,CMT(cold metal transfer)overlap process was used to conduct the overlap experiments on Al-steel bimetallic layer with the filler wire of ER4047 and ER7075.Hardness and tensile tests were conducted for mechanical property evaluation while microstructural analyses were consisted of optical microscopy and SEM.On this basis,the characteristics,porosity,contact angle and weld pool width of single-layer were characterized by metallographic analysis.In addition,the characteristics of single-layer of Al-Sn alloy deposited on Q235 steel plate was also studied tentatively.Results showed that the welding speed of 60 cm/min,wire extension of electrode of 4.0 mm,the welding voltage Avp of 90 % Ux,and the welding current of 50 A was the preferred overlap parameter for single-layer-single-pass overlap of Al-12Si/steel intermetallic overlap.With this preferred group of overlap parameters,welds showed an appearance of a balanced width,bright surface,high bonding strength and shear strength,while the interior of the welds showed a high porosities and poor wettability between the weld and the steel plate.Further experiments showed that the swing welding amplitude of 3.0 mm,the swing welding frequency of 2.5 Hz,the welding speed of 30 cm/min,the wire extension of 4.0 mm,the welding voltage Avp of 90% Ux,and the welding current of 65 A was the preferred welding parameter for single-layer-multi-pass overlap of Al-12Si/steel intermetallic overlap.With this preferred group of overlap parameters,welds showed a good performance of wetting behavior,high bonding strength and low porosities.When single-layer-multi-pass overlap was carried out with the welding current of 50-55 A,the superposition part of the second welding seam and the previous welding seam was micro-zone-melted due to the small welding heat input,the preferred weld spacing of single-layer-multi-pass overlap was 0.8-1.0 times to the weld width.When the welding current was between 55-70 A,the superposition part of the second welding seam and the previous welding seam was macro-zone-melted due to the high welding heat input,the preferred weld spacing of single-layer-multi-pass welding was 0.6-1.0 times to the weld width.For Al-4Zn/steel intermetallic overlap,the welding speed of 60 cm/min,the wire extension of 4.0 mm,the welding voltage Avp of 90 % Ux,and the welding current of 50 A was the preferred welding parameter for single-layer-single-pass overlap.The welds showed an uniform width,bright appearance,low porosity,good combination with steel plate and high shear strength deposited by this preferred group of overlap parameters.As for the swing welding process,the preferred process parameters are: swing welding amplitude of 3.0mm,swing welding frequency of 2.5 Hz,welding speed of 30 cm/min,wire extension of 4.0 mm,welding voltage Avp of of 90 % Ux and the welding current of 65 A.Deposited by this preferred group of overlap parameters,the width of welds was even and the surface was bright.However,it could not obtain a single-layer-multi-pass overlap layer,for which the presence of Zn element in Al-4Zn welding wire has a harmful effect on its wetting behavior and overlap characteristics.The IMC layer in the interface of Al-12 Si and steel plate showed an uneven thickness with a microstructure of flat micro-morphology near the steel side and serrated micro-morphology near the aluminum side,which indicating the growth direction of IMC was from the boundary to the aluminum side.On the welding interface of Al-4Zn and steel plate,the IMC layer presents a flat micro-morphology near the aluminum side,while it shows a serrated micro-morphology in the steel side.In the process of Al-Sn alloy overlap experiment,the agglomeration phenomenon of tin powder was serious during the overlap process with the method of spreading tin powder,and Al and Sn cannot be uniformly mixed in the overlap layer.In contrast,Al and Sn were uniformly mixed in the overlap layer obtained by the process of depositing the Sn layer,and the thickness of the Al-Sn alloy zone reached millimeter scale.However,both of the two overlap processes of Al-Sn alloy in this paper was only a preliminary exploration,and the experimental system with practical prospect has not been formed yet,which needs further studied in detail in the future.