Wetting And Brazing Of 70%SiC_p/Al Composites

Silicon carbide(SiC) particle reinforced aluminum matrix composites(SiC_p/Al) with high volume fraction(HFC, ≥50%) have a very broad application prospect in the field of electronic packaging, which are likely to replace the current kovar alloy to become a new generation of electronic packaging materials. However, it is quite difficult to join the HFC SiC_p/Al composites due to the great differences in physical and mechanical properties between the reinforcement and the matrix. Althrough several techniques involving melting welding, diffusion bonding, transient liquid phase bonding and brazing can realize the joining of the HFC SiC_p/Al composites, no one process can be skillfully used in the joining. Among which, brazing has a lot of potentials in the joining of HFC SiC_p/Al composite due to the relatively low brazing temperature, small welding deformation and low residual stress. In this dissertation, the Al-20Cu-6Si-x Mg(x=0、1、3、5, in wt.%) brazing filler metals with different norminal concentrations of Mg element were fabricated, and then the microstmctures, melting characteristic, phase composition, corrosion resistance and tensile strength of the four brazing filler metals were analyzed and discussed. Moreover, the wetting and brazing of 70 vol.%SiC_p/Al composite were investigated using the as-prepared Al-20Cu-6Si-x Mg and commercial Sn-3.5Ag-0.5Cu brazing filler metals.The experimental results showed that the Mg could react with Al to form low melting-point eutectic, which can lower the melting point of the Al-Cu-Si filler metal. The solidus and liquidus temperatures of Al-20Cu-6Si-x Mg(x=0、1、3、5) filler metals are 516.8 oC, 506.8 oC, 504.8 oC, 503.9 oC, and 534.3 oC, 531.9 oC, 529.8 oC, 531.4 oC, respectively. The Al-20 C u-6Si brazing filler metal mainly consisted of α(Al), Al2 C u and Al2 Si phases, and the Al-Cu-Si-Mg brazing filler metals were mainly composed of α(Al), Al2 C u, Al2 Si and Mg2 Si phases. Due to the good solid solution strengthening effect of Mg2 Si, the tensile strength of the Al-Cu-Si-Mg brazing filler metals was enhanced significantly and reached the maximum of 308.6 MPa after solid solution treatment. Moreover, the corrosion resistance of the sample decreased with increasing the Mg concentration due to thin oxidation film since the dissolution rate of Mg2 Si was faster than the formation of oxidation film.The wettability test showed that Mg can improve the wettability of the Al-Cu-Si brazing filler metal on the SiC_p/Al composite by removing the oxidation film on the surfaces of filler metals and base metal. The contact angles of the three Al-Cu-Si-Mg filler metals with 1%、3% and 5% Mg on the SiC_p/Al composites is 143.7°, 132.6°and 125.5°o, respectively. However, the Sn-3.5Ag-0.5Cu filler metal cannot wet the SiC_p/Al composite before N i electroless plating, but can well wet the N i-plated SiC_p/Al composite. The contact angle of Sn-3.5Ag-0.5Cu on the Ni-plated SiC_p/Al composite arrived at 19.4 o at 400 oC for holding 30 min.While brazing the SiC_p/Al composite using the Al-20Cu-6Si-x Mg brazing filler metals at 580 oC, the shear strength of SiC_p/Al composites brazed joints were 25.3, 33.6, 36.3 and 40.7 MPa, respectively; however, the shear strength of the N i-plated SiC_p/Al composite brazed joint using the Al-20 C u-6Si-5Mg brazing filler metal reached 75.2 MPa. The Sn-3.5Ag-0.5Cu filler metal almost can not directly braze the SiC_p/Al composites at 400 °C, but a good joint with the shear strength of 45.6 MPa can be obtained after the N i electroless plating.