| The aluminum-steel plate-fin heat exchanger, which has a series of advantages of the light weight, high heat efficiency and so on, has been widely applied in the field of chemical industry, automobile, aircraft industry, petrochemical engineering, power, medicine and metallurgy. It was brazed with steel-Al clad plate and aluminum plate-fin. However, the higher price of aluminum-steel cladding plates leading to high production costs. Steel plate and the surface coating of aluminum, stainless steel, which was the low-cost, was selected as the main experiment subject to solve the fatal matter. The mechanism of brazed with3003aluminum alloy and Q235steel,3003aluminum alloy and Q235steel sprayed aluminum used arc coating technology,3003aluminum alloy and lCr18Ni9Ti stainless steel, respectively, which were investigated in the light of the microscopic structure characteristics and element distribution in weld joint. The interface topography, phase composition and mechanism of weld connections were discussed. The conclusions of this paper are listed as follows:(1) The conditions Zn90Al4Ag5Ce at520℃solder on Q235steel and aluminum industries, connecting the shear strength decreases with holding time after the first increase in the holding time of5min, it is possible to a maximum of shear strength can be achieved17.6MPa; Zn90A14Ag5Ce aluminum brazing filler metal dissimilar steel soldered, on both sides of the base material has a good miscibility as aluminum/steel dissimilar metal brazing solder; in binding interface Q235steel weld zone and in the middle, because the affinity of Ag atoms and Al atoms in a strong, slow down the Al atom to the steel side of the diffusion rate, allowing harmful brittle zinc-aluminum solid solution phase grew slower conducive brazing to improve the mechanical properties of the welding head; weld zone of the aluminum combined with the intermediate interface, the zinc-rich solid solution of zinc-silver-white strip region on both sides of the Al atoms in the region having a larger concentration gradient, silver zinc solid solution having visible inhibition the ability of Al atoms diffused into the steel side.(2) Under the conditions of260℃solder while using Sn90Ag5Ti5ultrasonic vibration assisted to achieve arc spray Q235steel and aluminum industrial aluminum, connecting with the shear strength after prolonged ultrasonic vibration increases after the first change, when vibration time40s, to the maximum possible value of shear strength can be achieved14.3MPa. Ultrasound-assisted welding main role is to remove the surface oxide film and improve the performance of solder wet ability, and prompted liquid solder coating to aluminum penetration hole parts, improved solder and aluminum coating bonding area is conducive to welds improving the strength. Under no circumstances ultrasonic assisted, can not realize the connection between the two; due to the low temperature brazing, diffusion brazing filler metal and the sides are not obvious; weld area Ti6Sn5played dispersion strengthening effect is generated in order to improve the welding metal seam strength; brazing process, the weld zone with a small amount of oxidation.(3) Using A174.5-Cu17.2-Mg8.3(mole fraction) to form a ternary eutectic this principle, lCr18Ni9Ti were plated on nickel, copper, wherein the copper plating layer having a thickness of20μm, Mg in an amount of0.01g/cm2at brazing temperature560℃,holding time15min, under heavy pressure to achieve2Kg aluminum and stainless steel reaction brazing; contact reaction of aluminum and stainless steel welded joints brazed shear test, to get the maximum shear strength of21.6MPa; Al atomic diffusion is more obvious in the weld region, has a greater concentration of the intermetallic compound is formed and Al-Cu, Al-Mg, Al-Fe-based and so the entire weld area. |
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