Interface and Properties of Aluminum/Steel Composite Plates with Different Covering Temperature
According to the needs of various industries in society for materials,a single material has been unable to meet the perfor-mance requirements,composite materials appear to solve the compatibility problem of material properties.Bimetal composite plate combines the advantages of two kinds of metal materials and makes up their disadvantages to meet the requirements of modern indus-try.The purpose of this paper was to develop the best material preparation technology to make the excellent performance of the two com-ponents maximize the coordination for composite plate.6061 aluminum alloy had the characteristics of low density,good corrosion re-sistance,good conductive and thermal conductivity,and Q235 low carbon steel had the characteristics of low price,high strength,wide application,and the deformation of the two materials was excellent,so this paper selected these two materials as composite plate components.The cast-rolling process technology for aluminum/steel bimetal composite plates could obtain the organization of dense and metallurgical bonding interface,covering temperature could be controlled in combination with the amount and type of intermetallic compound interface,therefore,the effects of different covering temperatures of 6061 aluminum alloy on the interface microstructure and mechanical properties of composite plate were studied in this paper.The preparation process of composite plate:Q235 steel plate was cut,polished and cleaned as the substrate,and the pre-treated substrate was placed in a resistance furnace for preheating.Melting all 6061 aluminum alloy ingot,refining,then adjusting the temperature to 730,710,690,670 and 650 ℃,respectively,the molten 6061 aluminum alloy with adjusted temperature was poured onto the preheated Q235 substrate,and started solid-liquid cast-rolling,the thickness of the rolled composite plate was 3.3 mm,Q235 substrate layer was 1 mm,and 6061 aluminum alloy layer was 2.3 mm.Optical microscope(OM)and field emission scanning electron microscope(SEM)were used to observe the interface microstructure of the composite plate,energy dispersive spectroscopy(EDS)was performed for micro component analysis,X-ray diffractometer(XRD)was used to analyze the interface intermetallic compound,microhardness tester was used to measure hardness changes near the inter-face,and universal material testing machine was used to test mechanical properties.The microstructure of the composite plate inter-face showed that when the covering temperature was 650 ℃,there was no obvious diffusion layer at the interface of the composite plate,with the increase of the covering temperature from 650 to 730 ℃,the grain size at the interface of Q235 substrate increased gradually,when the covering temperature was 710 ℃,the thickness of the diffusion layer was 5.2 μm,and when the covering temper-ature was 730 ℃,the thickness of the diffusion layer was 5.9 μm.The interface between the diffusion layer and the side adjacent to the aluminum alloy remained smooth,and the interface between the diffusion layer and the side of the substrate gradually formed"ser-rated"interface.The analysis of interface composition and element distribution of composite plate,the intermetallic compounds such as Al,Fe2 and Al3Fe were found to form at the interface by XRD and EDS spot scanning.By testing the hardness near the interface of composite plate,the hardness of interface was between Q235 substrate and 6061 aluminum alloy,when the covering temperature was 650 ℃,the interface hardness was relatively low,when the covering temperature was 730 ℃,the number of intermetallic compounds formed at the bonding interface was the largest,and the microhardness at the interface was the highest,reaching HV 120,and the hardness on one side of the substrate decreased slightly with the increase of the covering temperature,while the hardness on the side of 6061 aluminum alloy did not change greatly.The results of mechanical properties test showed that the tensile strength and shear strength of the composite plate firstly increased and then decreased with the increase of the covering temperature,when the covering temperature was 710 ℃,the mechanical properties of the composite plate was the best,the thickness ratio of aluminum to steel was 2∶1,the tensile strength was 233 Mpa,the elongation at break was 25.5％,and the shear strength was 92.5 Mpa,the maximum tensile strength of cast-rolled 6061 aluminum alloy sheet was 140 Mpa,compared with cast-rolled 6061 aluminum alloy sheet,the tensile strength of composite plate had increased by 66.4％,when the covering temperature of 6061 aluminum alloy was 690 ℃,the maxi-mum elongation of composite plate was 28％.By observing the shear fracture morphology of the composite plate,it was found that a large number of pits and tear edges were formed on one side of the aluminum alloy section,and convex points corresponding to the pits were formed on Q235 side,EDS did not detect Fe on 6061 aluminum alloy side,and the fracture mainly occurred on the aluminum al-loy rather than the bonding surface,which indicated that the interface of the composite plate was well bonded.
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