Microstructure and Properties of the Al-27Si/Cu/Al-50Si Joint Brazed by the Partial Transient Liquid Phase Bonding
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-Si alloys belong to the metal matrix composite materials in which Si phases are embedded in the a-Al matrix.[1] Owing to the composite structure and the presence of primary Si particles, these alloys possess excellent integrated properties, such as low thermal expansion coefficient, high thermal conductivity, low density, good wear resistance, and corrosion resistance.[1–7] These advantages make Al-Si alloys to have wide applications in electronic packaging, aerospace, machinery/heavy, and automotive industry.[2–4] In particular, an ultra-high silicon Al-50Si alloy (Al-50Si) is often used as the packaging box materials for integrated circuit seal and signal transmission,[8] and the corresponding box cover is made of Al-Si alloy with lower silicon content, such as the Al-27Si alloy (Al-27Si). These two high silicon Al-Si alloys with different silicon contents usually need to be welded together for the entire packaging box. The coarse flake-like Si particles are easily formed in the Al-Si matrix at elevated temperature during welding process, and which show detrimental effects on the
QINGZHU SUN, HAIBO WANG, and CHENG YANG are with the Panzhihua International School of Vanadium and Titanium, Panzhihua College, Panzhihua, 617000, P.R. China. Contact e-mail: [email protected] Manuscript submitted October 31, 2017. METALLURGICAL AND MATERIALS TRANSACTIONS B
mechanical properties of these materials.[6] Therefore, two commonly low-temperature joining techniques, brazing and friction stir welding, are usually utilized to join these Al-Si alloys.[9–12] Sekulic studied the dendritic growth behaviors in Al-7Si solders during brazing and found that many dendrites of the primary Si phase were existed in the brazing seam due to the higher brazing temperature (> 600 C).[9] A series of Al-Si alloys with moderate silicon content have been successfully welded by friction stir welding, such as A356 alloy[10,11] and Al-12Si alloy.[12] However, studies on the welding of ultra-high silicon Al-Si alloys have seldom been reported. Therefore, it is significant for the electronic packaging industry to explore the joining behaviors of the ultra-high silicon Al-Si alloys. Partial transient liquid phase bonding may be a feasible alternative for these high silicon Al-Si alloys, because lower bonding temperature and shorter bonding time can be achieved by selecting appropriate interlayer.[13] Cu is widely used as an alloying element to promote the formation of semi-coherent CuAl2 precipitates in Al alloys,[14] and the eutectic temperature is only 524 C according to the Al-Cu-Si ternary phase diagram.[15] Therefore, we choose Cu as interlayer to bond the Al-27Si and Al-50Si; the microstructure and properties of the Al-27Si/Cu/Al-50Si joint are investigated in the present study. Al-27Si and Al-50Si were prepared via the OSPREY spray casting process, and this process was described in detail elsewhere.[16] In the spray casting process, commercially pure Al powder (average particle size 14 mm, 99.95 pct purity) and Si powder (average particle size 5 mm, 99
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