Study on Characteristic of Aluminum Base Filler Metal with Low Melting Point and Salt Bath Brazing
|School||Lanzhou University of Technology|
|Course||Materials Processing Engineering|
|Keywords||aluminum base filler metal salt bath brazing 6063aluminum alloy shearstrength|
Aluminum alloy is a most suitable material for light weighting of vehicles ofaviation and aerospace system while brazing is one of the most universal methods toweld aluminum alloy. Al-Si based filler metal has been widely used in industry due toits good wettability, fluidity, mechanical properties and corrosion-resistance ofbrazing joint. However, its melting point is very high(eutectic point is577℃) andclose to the base metal which makes it always very hard to control weldingtemperature and consequently leads to mechanical property of the brazing joint worse.This has become a technique bottleneck restricting the application of aluminumbrazing. In this paper, in order to reduce the melting point of Ai-Si brazing filler,based on Ai-Si brazing filler, Cu is a key element of reducing the melting point of thesolder, Zn and Sn not only reduces the temperature of the solder fusion, but alsoincreases the wettability and the fluidity of the solder, in order to further bring downthe melting point and improve the good technology properties and mechanicalproperties.In this paper, a series of A1-Si-Cu-Sn-Zn filler metals was developed for brazingsome alloys and the vacuum induction melting furnace is used to prepare the lowmelting point filler metals. The melting point, wettability and fluidity of the solderwere measured through DSC, wetting properties and filling test, ruled out the formulado not meet the requirements. The microstructure was analyzed by the opticalmetallographic microscope, XRD, EPMA etc. Through the salt bath brazing method,the shear strength of solder were determined and analyzed. The new and reasonablelow melting point of aluminum brazing filler metals was developed, and its formulawas Al72Si6Cu15Zn4Sn3.The result shows that: The solder melting point of newaluminum brazing filler metals is521.0℃, less56℃than the solder melting point ofAi-Si brazing filler, and the melting temperature range is limited; Further, it has agood wettability and fluidity in560℃, therapid solidification solder havewell-distribution of elements and fine crystal grain, and it can braze6063aluminumalloy in560℃, and it enables the strength of brazing to become more the strength ofbase metal of80%.The micro-analysis was made with the use of metallographicmicroscope, X-ray diffraction and electron probe. Welds composition with newsolders are well distributed with fine joint reaction, by which the new solder shows itsgood flowing clearance filling capacity. In the contact reaction, the copper spreadsquickly into the raw matericals. It also can be used to braze6063aluminum and some forged aluminum alloy, which is an ideal solder of the salt bath brazing of the forgedaluminum alloy.