Self-fluxing brazing alloy for brazed connection of PTC ceramic and aluminum alloy and preparation method of self-fluxing brazing alloy

Abstract

The invention provides a self-fluxing brazing alloy for brazed connection of PTC ceramic and aluminum alloy and a preparation method of the self-fluxing brazing alloy. The self-fluxing brazing alloy is prepared from the following raw materials in percentage by weight: 2% to 6% of Al, 0.06% to 0.18% of In, 0.01% to 0.12% of Ti, 4% to 8% of Bi, 0.4% to 0.8% of P, 0.02% to 0.3% of KF, 0.01% to 0.2% of RE and the balance Zn, wherein RE represents La, Pr, Er, Dy or Nd. The preparation method comprises the following steps: preparing mother alloy by using all of the components according to a specified weight percentage; putting the mother alloy in a graphite crucible, and performing induction heating and remelting in a vacuum furnace; spray-casting molten liquid alloy on a high-speed rotating red copper roller by using argon after the mother alloy is heated to the temperature of 850 to 1000 DEG C; and performing shock cooling to obtain a solder foil band. The self-fluxing brazing alloy has certain plasticity in a solid state, has good wettability to the PTC ceramic, can be bonded with a PTC ceramic interface, and satisfies the requirement of the working temperature (smaller than or equal to 300 DEG C) of the PTC ceramic.

Description

technical field [0001] The invention belongs to the technical field of brazing materials, and in particular relates to a self-brazing filler metal for brazing and connecting PTC ceramics and aluminum alloys and a preparation method thereof. Background technique [0002] The total amount of aluminum alloys for industrial use has exceeded 2 million tons in 2009, and the amount used by the automotive industry alone has reached 1.3 million tons. Among the aluminum alloy structural parts used in the above-mentioned equipment, about 15-20% of the aluminum alloy structural parts are formed by brazing. According to the average consumption rate of brazing of 1%, the demand for aluminum-based solder for aluminum brazing is about It is 3000-4000 tons. [0003] The current method of connecting PTC ceramics and aluminum alloys is mainly to use glue bonding. Since the working temperature of PTC ceramics can reach up to 300 ° C, the process of using silica gel bonding has the following di...

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Problems solved by technology

[0003] The current method of connecting PTC ceramics and aluminum alloys is mainly to use glue bonding. Since the working temperature of PTC ceramics can reach up to 300 ° C, the process of using silica gel bonding has the following disadvantages: 1) Silica gel is easy to age during use, resulting in the deterioration of PTC ceramics. Power drops, which can lead to component damage in severe cases; 2) Due to the poor electrical and thermal conductivity of the silica gel in the joint layer, the role of PTC ceramics cannot be fully utilized; 3) The long-term stability and reliability of the joint glued with silica gel is poor; 4) Silicone During use, it will emit a peculiar smell when heated

Due to the addition of a large amount of Al, Zn72Al28 solder has a high melting point (430-500 ° C), which is not suitable for brazing PTC ceramics; Zn95Al5 is a solder with eutectic point composition, and its melting point (Tm = 380 ° C) is more suitable, but the solder It is brittle, and when brazing PTC ceramics, a large internal stress is generated, and at the same time, the wettability of PTC ceramics is poor, and the bonding ability is weak, resulting in poor joint strength; Zn65Al20Cu15 is based on Zn-Al, adding Cu to reduce the melting point (415 ~ 425 ℃), but the content of Al and Cu is too high, the brazing filler metal is brittle, the brazing filler metal also has poor wettability to PTC ceramics, and the bonding ability is weak; Zn93Ag4. The wettability and corrosion resistance of the solder mentioned above are poor for PTC ceramics, the solder is brittle, the bonding ability is weak, and some melting temperatures are too high. After brazing connection, a large internal stress is generated. , so that the bonding strength is reduced, which cannot satisfy the connection of PTC ceramics

No. 02133083.2 Chinese invention patent application "Self-brazing filler metal for aluminum alloys and aluminum-based composite materials and its preparation method" proposes a formula for medium-temperature, high-strength, flux-free brazing materials for aluminum alloys and aluminum-based composite materials. In terms of alloying elements, the melting point is higher than 400°C. This solder is used for brazing of aluminum alloys and aluminum matrix composite materials, and has superior performance. However, due to the high melting point alloy elements (to ensure strength), the solder has a higher melting point , also not suitable for the connection of PTC ceramics