Translated Abstract
Hybird structures of aluminum alloy and steel have the comprehensive benefits of light weight and high strength, they have played an important role in promoting the lightweight process of vehicle body. However, there are great differences in physical properties between aluminum alloy and steel, the solid solubility of iron atoms in aluminum is low, and brittle intermetallic compounds are easy to formed in the joint, it’s difficult to connect them with traditional welding methods. Nowadays, welding-brazing with the characteristics of convenient operation and high efficiency offers a great potential for material combinations of aluminum alloy and steel, this method can avoid the melting of steel material.
In this study, the thickness of parent material is 2 mm, the laser welding-brazing with precoated flux layer method was used to connect 6061-T6 aluminum alloy and SPCC cold rolled steel butt structure, we obtain hybird joints with dual characteristics of welding and brazing, we prefabricate groove with different angles and morphology for steel material, we also change the components of precoated flux layer and brazing filler metal, the differences in interface structures and mechanical properties of brazing joints were researched. The research results have reference value for the application of laser welding-brazing of aluminum alloy to steel.
The precoated Nocolok flux layer can improve the wettability of liquid solder on the surface of steel material greatly, when filling aluminum magnesium, aluminum silicon, aluminum copper wire, the spreading length of liquid molten pool on the surface of steel material improve 46.5%, 131.1% and 127.4% compared with no flux layer.What’s more, the precoated flux layer also play the role of heat barrier and chemical barrier, the melting of steel material and the diffusion of iron atoms into molten pool have been weakened.
When the prefabricate groove angle of steel material is 60 degrees, and the laser power, welding speed, wire feeding speed, laser defocus, offset center of the laser spot center are 3100W, 0.5m/min, 2m/min, -8mm, +0.6mm, respectively, with ER2319 Al-Cu filler metal, the average and maximum tensile strength of the joint are respectively 147.1MPa and 159.2MPa, the interface layer presents short whisker shape and consists of FeAl, FeAl2 and (Fe,Cu)4Al13 phase, the interface layer is in 5~8μm thickness, the Cu element is dissolved in Al-Fe brittle phase by replacing Fe elements to reduce its brittleness.
With ER5356 Al-Mg filler metal, the average tensile strength of the joint is 117.5MPa when the laser power is 3000W, the interface layer presents coarse sawtooth shape consists of FeAl2, Fe2Al5 and FeAl3 phase, the interface layer is in 8~12μm thickness, the Mg element is gathered at the outside of brittle phase, and it has no obvious inhibitory effect on the growth of Al-Fe brittle phase; with ER4043 Al-Si filler metal, the average tensile strength of the joint is 128.9MPa when the laser power is 3000W, the interface layer presents small sawtooth shape consists of FeAl2 and FeAl3 phase, the interface layer is in 3~4.5μm thickness, the Si element is dissolved in Al-Fe brittle phase to inhibit its growth.
Translated Keyword
[Heat treatment, Laser additive manufacturing, Modification treatment, TC4]
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