Effects Of Intermediate Layer On Interfacial Microstructures And Properties Of A356/2024 Laminated Aluminum Matrix Composites

The laminated metal composite is a new kind of composite material,which combines two or more metals with different ph ysical,chemical and mechanical properties to realize firmly and stably bonding at the interface b y combined process.Compared with single metal material,the laminated metal composites have a unique"complementary effec t",which can combine the specific characteristics of different metal lic compositions in order to meet the stringent requirements under special circumst ances.It is also due to the unique properties of composites with multi-components that the application of laminated metal composites has been widely used in aerospace,electronic power,petrochemical industry,building decoration,aut omobile,ship and other fields.This paper focuses on the study of adding different interlayer metals to the interface of laminated Al-matrix composites,using interlayer metals a s interfacial transition layer to improve the wettability of interface and inhibit the diffusion of alloy elements,in order to solve the problem of stress concentration and the formation of hard and brittle intermetallic c ompounds at the interface of composites.The laminated Al-matrix composites was prepared by liquid-solid roll casting technology and replaced the oxide film on 2024aluminum substrate by zinc,nickel and copper intermediate layers.Then through anal ysis on the surface morphology,chemical composition and growth model of zinc,nickel and copper layers on 2024 aluminium substrate,and compared with the effects of different interlayer metals and A356 aluminium melt pouring temperatures on the interfacial structure and properties of composite samples.The following conclusions were obtained through comprehensive analysis:?1?Due to the particularity of ph ysical and chemical properties of aluminum allo y,secondary zinc coating is required to obtain good bonding metallic coating.When preparing Zn coating,it is found that Zn particles are closely stacked on the surface of aluminum substrate.With the prolongation of plating time,the thickness of Zn coating becomes thicker and the coverage of aluminum substrate increases.Howeve r,the corresponding Zn coating will grow preferentially in the local area,resulting in uneven surface of Zn coating and deteriorated the coating qualit y.Comparing the surface morphology of Zn coating with 10,15 and 20mins,the surface quality of Zn coating obtained at10mins is the best,and the cross-section thickness of Zn coating is about 5-6?m.The Ni and Cu coatings are ellipsoidal on the surface of aluminum substrate,and the crystal cell size of the Ni coating is much smaller than that of the Cu coating.?2?By compar ed and analyz ed the microstructure,composition distribution,element diffusion and XRD test of interface between A356/2024 and A356/Zn/2024 composite specimens,it i s eas y found that the zinc interlayer does not react with the alloy e lements in the aluminum matrix and not form hard and brittle phases to deteriorate the interface bonding strength.The main function of the zinc interlayer is to replace the inherent oxide film on the surface of 2024 aluminum substrate and to impr ove the heterogeneous aluminum wettability between interfaces.?3?By compared and analyzed the interfacial microhard ness distributions of A356/2024 and A356/Zn/2024 composite specimens.It is found that the hardening phases,such as?-Al₂Cu and S-Al₂CuMg phases,often formed on the surface of 2024 aluminum substrates.The existence of hardening phases would lead to the hardness peaks located on the side of 2024 aluminum substrates rather than on the interface region.The significance of Zn interlayer is onl y to im prove the wettability between solid-phase Al-substrate and Al-melt,and to form a wider and deeper melting zo ne on the contact surface of Al-substrate,thus lead to form more hardened phase on the side of Al-substrate.?4?The effect of pouring temperature of A356 aluminium melt on the interfacial shear strength of composites is different.When the pouring temperature of aluminium melt is higher,the surface zinc treatment can obviously enhance the interfacial shear strength,which is beneficial to play the role of zinc interlayer as protective film and improve w etting.At the pouring temperature of aluminium melt is 700?,the interfacial shear strength of composite specimens increases from 100 MPa when the surface is not treated b y zinc plating to 141 MPa when the surface is treated by zinc plating,the shear strength increase d by 40%.When the pouring temperature is low,the surface zinc treatment will restrict the interfacial shear strength of composite samples.The semi-solid state of A356 aluminum m elt will play a leading role in the interfacial shear strength of composite samples.Especially,when the pouring temperature of A356 aluminum melt is 610?,the interfacial shear strength of A356/2024 composite samples reached 153MPa even without zinc interlayer,which is the highest value in the experimental group.?5?Because of the rapid prototyping of roll casting technology,the contact time between high temperature Al-melt and Ni,Cu interlayer is limited,which results in the diffusion of Ni and Cu el ements hindered and remains at the interface,unlike that of Zn elements could occur miscibility and diffusion.Although the eutectic reaction temperature between Al-Ni and Al-Cu is lower than the pouring temperature of A356 aluminum melt,while the melting points of Ni and Cu elements are relatively high.The heat of high-temperature aluminum melt can not be directly transferred to the sur face of aluminum matrix,only rel y on the weak diffusion reaction to complete the interfac e bonding.This bonding metho d must not have high bonding strength of metallurgical bonding,and ultimately leads to A356/Ni/2024,A356/Cu/2024composite specimens interfacial shear strength decreased.