Monitoring Experiment And Simulation For Brazing And Bonding Of Aluminum Alloy And Steel Based On Optical Fiber Sensing Technology

The quality of aluminum alloy and stainless steel dissimilar metal(Al/steel) joint is influenced by the internal temperature and strain during the fabrication process, thus the real-time monitoring for the fabrication process is beneficial to effectively improve the processing technology. In this paper, monitoring experiment and simulation investigation for the Al/steel brazing and bonding processes based on optical fiber sensing techonogy were systematically conducted and the associated results were listed as follows:Metallization enhanced sensitivity and protection for fiber Bragg grating(FBG) was presented by using the electroless plating and electroplating method, and the temperature and strain coefficients of metallized FBGs were calibrated. The temperature and strain sensitivity coefficients of FBGs after metallization of electroless Ni plating and Ni electroplating(#1FBG), electroless Cu plating and Cu electroplating(#2FBG), electroless Ni plating and Cu electroplating(#3FBG) were KT1 = 20.17pm/oC, KT2 = 28.68pm/oC, KT3 = 30.69pm/oC and Kε1 = 1.7pm/με, Kε2 = 1.8pm/με, Kε3 = 2.5pm/με, respectively.The wettability and spreadability of AlSi12 eutectic filler metal on 6061 aluminum alloy and 316 L stainless steel was studied. The compact brazed joint of 6061/ AlSi12/ 316 L was obtained at the temperature of 600oC. The embedment of the FBG after electroless Ni plating and Ni electroplating and the FBG after electroless Ni plating and Cu electroplating into 6061/ AlSi12/ 316 L brazed joint were satisfactorily implemented.The real-time monitoring for the temperature and strain evolution within the Al/steel bonding joint during the curing process was realized, and the maximum values of temperature rise and shrinkage strain were ΔT = 33.96oC and Δε =-21.73με, respectively.Two finite element models on the sensing monitoring were established, which were used to analyze the response of the matel materials with surface brazed FBG to the thermal load during the brazing process and subjected to load after metallization.Two finite element models were established in ANSYS software and the associated simulation analyses were conducted. The simulated value of wavelength drift for sensing monitoring during the brazing process for embedding the metallized FBG into the surface of metal material(316L stainless steel) was ΔλB =-6.94nm; and metal material embedded with FBG had the ability to response to the given load and the strain sensitivity coefficient was Kε = 1.3pm/με. The simulated value of wavelength drift for sensing monitoring during the brazing process for embedding the metallized FBG into the U-groove of metal material(6061 aluminum alloy) was ΔλB =-12.1nm.