The Formation Mechanism Research Of Fe/AL Dissimilar Materials Bonding Iterface

Aluminum and aluminum alloys have the good physical and chemical properties, whilestainless steels have the properties of high strength, welding, corrosion resistance andthermal stability etc. Synthesizing the excellent properties of aluminum alloys and stainlesssteel to make full use of resources, it has the good economic efficiency. The joint betweenaluminum alloys and stainless steels will be easy to generate the Fe-Al brittle intermetallics.According to the results of microstructure observed, the relation betweenmicrostructure and diffusion behavior of element near the interface for Fe/Al diffusionbonding was analyzed,which helpful seek the relation between interfacial transition zoneformed and element diffusion.It is very valuable to improve the joint between aluminumalloy s and stainless steels.The microstructure in the transition zone of Fe/Al dissimilar metal was analyzed bymetalloscope and scanning electron microscope （SEM） The distribution of microhardness ininterface of Fe/Al diffusion bonded-joint was analyzed by microhardness tester. Theexperiment results indicated that intermetallic thickness grows in the form of main gear, thethickness of the compound layers increased with parabolic cure rule; Reaction area existeddouble structure at560℃for0.5h; Reaction layer thickness increased with the extensionof time, as holding time reached a certain value, the reaction layer thickness no longerincreased; the obvious micro-cavitas existed near the transition zone of Al side, whoseorganization was relatively loose, with the welding process parameters increasing, crack inthe transition layers of aluminum side will appear; There were three different hardness（range from626¹078HV） distribution in the diffusion reaction zone.The phase constitution of Fe/Al welding zone and distribution of elements in transitionzone by means of X-ray diffraction（XRD）and electron probe microanalysis（EDS）.The testresults indicated that elements concentration existing three concentration distribution areasat interface of Fe/Al joint, decreased from base metals to interface transition zone; Theintermatallic compounds FeAl₂、FeAl₂、FeAl、FeAl₂were formed in the interfacialtransition zone, the layer thickness of FeAl₂compound layer at Al side was the widest, thenthe FeAl₂,a little of FeAl and FeAl₂existed near the Fe side.The formation of interfacial transition zone for Fe/Al diffusion bonding included fourstages. Firstly,FeAl compounds formed at Al side, the unstable FeAlx generated at Fe side,finally FeAl₂,FeAl₂,FeAl and FeAl₂appeared.The formation rate of which wasνFeAl₂<νFeAl<νFeAl₂<νFeAl₂<νFeAl₂.According to Boltzmana-Matano method, the relation equation of diffusion coefficient（D） and element concentration （C） of Fe and Al elements in interfacial transition zone wasdetermined for Fe/Al diffusion bonding. The diffusion coefficient of Fe and Al atoms in theinterfacial transition zone can be obtanined. The results indicated that with the increase ofthe heat temperature and element concentration the diffusion coefficient of Fe and Al atomsincreased, the diffusion capacity of Fe was weaker than Al. Using diffusion coefficient （D）and error function, it can be obtained the reaction diffusion equation of elements in theinterfacial transition zone, The results indicated that the measured result of diffusion withfor the interfacial transition zone was smaller. The width for calculation result was moreclose to the measured value through the Al element calculation. There are certain relationsbetween the transition zone width of each phase of Fe/Al diffusion joint and holding time.With the dynamic analysising that the formation of intermetallic needs a certain latent periodt0, and t0will reduce with the increase of heating temperature.