A brazing process for high-silicon aluminum alloy hole assembly parts

Abstract

The present invention discloses a brazing process for high-silicon aluminum alloy hole assembly parts. The process comprises the following steps: plating Ni-P layers and Au layers on the surface of the parts, adopting Au80Sn20 eutectic solder for welding, controlling the temperature rise in a stepwise manner, and controlling the cooling rate to ensure that the parts and the solder are heated evenly, thereby reducing stress and deformation caused by uneven temperature distribution on the workpiece, avoiding welding cracks and defects such as Si cracks in the raw materials, and strictly controlling the volume ratio of the weld to the solder to effectively eliminate solder overflow and weld voids, thereby ensuring welding quality.

Description

Technical Field

[0001] The invention relates to a brazing process, in particular to a brazing process for high-silicon aluminum alloys. Background Art

[0002] The brazing process involves filling the weld gap with a low-melting-point brazing filler metal. Heating the filler metal fills the gap and welds the two parts together. Generally, the parts have good brazing wettability, which can well meet welding requirements. High-silicon aluminum alloys have advantages such as low expansion coefficient, low density, high strength, high thermal conductivity, easy processing, and good plating properties. They are widely used as shells for packaging structural parts in fields such as aerospace and modern electronic information technology. However, due to the large amount of hard Si phase in high-silicon aluminum alloys, the wettability of the brazing filler metal on the alloy surface deteriorates, making it difficult for ordinary soft soldering to meet welding requirements. To improve brazing performance, an article titled "Interface Reaction of Au80Sn20 Eutectic Brazing Filler Metal and Ni / Au Coating in Brazing" was published in the journal "Electric Welding Machine" Vol. 50, Issue 2, February 2020. The article used a Ni layer and an Au layer to be plated on the surface of a high-silicon aluminum alloy, and then brazing was performed using AuSn eutectic brazing filler metal. However, this brazing process is prone to defects such as solder overflow, weld voids, weld cracks and raw material cracks after welding is completed, making it difficult to ensure the brazing quality. Summary of the Invention

[0003] In order to solve the defects of high silicon aluminum alloy brazing process in the prior art, such as solder overflow, weld voids, welding cracks and raw material Si cracks, the technical solution adopted by the present invention is:

[0004] A high-silicon aluminum alloy hole system assembly brazing process comprises the following steps:

[0005] s1. Material selection: Select silicon-aluminum alloy with silicon content of 30% to 70%, and Au80Sn20 eutectic solder;

[0006] s2. Surface treatment: plating Ni-P layer and Au layer on the surface of silicon aluminum alloy parts in sequence;

[0007] s3. Prepare the brazing filler metal: Prepare the brazing filler metal into the weld of the silicon-aluminum alloy parts to be welded, so that the volume ratio of the brazing filler metal to the weld is 0.85-1.25;

[0008] s4. Place the parts with brazing filler metal into the vacuum furnace and evacuate to 10 ～2 Pa;

[0009] s5. Maintaining vacuum, raise the temperature to 150-180°C at a rate of 1-2°C / s and keep warm for 5-10 minutes;

[0010] s6. Fill the furnace with nitrogen until the pressure inside the furnace is between 30 and 90 kPa, and heat it to 250-270 °C at a rate of 1-2 °C / s, and keep it warm for 1-5 minutes;

[0011] s7. Raise the temperature to 310-350℃ at a rate of 1-2℃ / s and keep warm for 30 seconds to 3 minutes. After the insulation is completed, immediately evacuate to below 10Pa, then quickly fill with nitrogen and cool to below 250℃ at a rate of 1-2℃ / s. Remove from the furnace and air cool.

[0012] Furthermore, the Ni-P layer is formed by chemical plating, and the Au layer is formed by electroplating.

[0013] Furthermore, the thickness of the Ni-P layer is 3 to 15 μm, and the thickness of the Au layer is 0.5 to 5 μm.

[0014] Furthermore, the silicon-aluminum alloy parts and solder are ultrasonically cleaned in an anhydrous ethanol solution for 8 to 10 minutes before being loaded into the furnace, and then dried with nitrogen before the solder is prepared.

[0015] This process controls the heating and cooling rates to ensure that the parts and the solder are heated evenly, reducing stress and deformation caused by uneven temperature distribution on the workpiece, avoiding welding cracks and cracks in the raw materials. The volume ratio of the solder to the weld can effectively eliminate solder overflow and weld voids, thereby ensuring welding quality. DETAILED DESCRIPTION

[0016] The following three examples further introduce the high silicon aluminum alloy brazing process:

[0017] The chemical composition of the high-silicon aluminum alloy parts is as follows: Si: 50.5%, Fe: 0.13%, Zn: 0.02%, Ca: 0.02%, Sn: 0.018%, Pb: 0.012%, Al: balance. The brazing filler metal is Au80Sn.

[0018] Example 1

[0019] During the workpiece and solder preparation stage, the silicon-aluminum alloy parts and solder are ultrasonically cleaned in an anhydrous ethanol solution for 8 minutes and then blown dry with nitrogen to ensure that the brazing interface is clean and pollution-free, and to avoid the influence of surface impurities on the welding quality.

[0020] Surface treatment: Ni-P layer and Au layer are plated on the surface of silicon aluminum alloy parts in sequence; the Ni-P layer is chemically plated to a thickness of 4μm, and the Au layer is electroplated to a thickness of 1.2μm;

[0021] Prepare the brazing filler metal: Place the brazing filler metal into the welding gap of the silicon-aluminum alloy parts to be welded, so that the volume ratio of the brazing filler metal to the weld is 0.85;

[0022] Place the parts with brazing filler metal into the vacuum furnace and evacuate to 10 ～2 Pa;

[0023] Maintaining vacuum, the temperature was raised to 180°C at a rate of 1°C / s and kept at this temperature for 5 minutes;

[0024] Fill the furnace with nitrogen until the pressure inside the furnace reaches 90 kPa, raise the temperature to 270 °C at a rate of 1 °C / s, and keep it at this temperature for 3 minutes;

[0025] The temperature was raised to 330°C at a rate of 1°C / s and kept at that temperature for 40 seconds. After the holding period, the vacuum was immediately evacuated to below 10Pa, and then nitrogen was quickly filled and the temperature was lowered to 220°C at a rate of 1°C / s before being taken out of the furnace and air-cooled.

[0026] After welding is completed, the surface consistency is good, the airtightness test is qualified, the weld structure is dense, and there are no defects such as bubbles and voids.

[0027] Example 2

[0028] In the workpiece and solder preparation stage, the silicon aluminum alloy parts and solder were ultrasonically cleaned in anhydrous ethanol solution for 10 minutes and then dried with nitrogen gas as in Example 1 to ensure that the soldering interface was clean and free of contamination and to avoid the influence of surface impurities on the welding quality.

[0029] Surface treatment: Ni-P layer and Au layer are plated on the surface of silicon aluminum alloy parts in sequence; the Ni-P layer is chemically plated with a thickness of 5.3μm, and the Au layer is electroplated with a thickness of 3.2μm;

[0030] Prepare the brazing filler metal: Place the brazing filler metal into the welding gap of the silicon-aluminum alloy parts to be welded, so that the volume ratio of the brazing filler metal to the weld is 1.25;

[0031] Place the parts with brazing filler metal into the vacuum furnace and evacuate to 10 ～2 Pa;

[0032] Maintaining vacuum, the temperature was raised to 180°C at a rate of 1°C / s and kept at this temperature for 8 minutes;

[0033] Fill the furnace with nitrogen until the pressure inside the furnace reaches 80 kPa, heat it to 250 °C at a rate of 1 °C / s, and keep it at that temperature for 2 minutes;

[0034] The temperature was raised to 310°C at a rate of 1°C / s and kept at that temperature for 1 minute. After the holding period, the vacuum was immediately evacuated to below 10 Pa, and then nitrogen was quickly filled and the temperature was lowered to 200°C at a rate of 1°C / s before being taken out of the furnace and air-cooled.

[0035] After welding is completed, the surface consistency is good, the airtightness test is qualified, the weld structure is dense, and there are no defects such as bubbles and voids.

[0036] Example 3

[0037] In the workpiece and solder preparation stage, the silicon aluminum alloy parts and solder were ultrasonically cleaned in anhydrous ethanol solution for 10 minutes and then dried with nitrogen gas as in Example 1 to ensure that the soldering interface was clean and free of contamination and to avoid the influence of surface impurities on the welding quality.

[0038] Surface treatment: Ni-P layer and Au layer are plated on the surface of silicon aluminum alloy parts in sequence; the Ni-P layer is chemically plated with a thickness of 3.9μm, and the Au layer is electroplated with a thickness of 0.85μm;

[0039] Prepare the brazing filler metal: Place the brazing filler metal into the welding gap of the silicon-aluminum alloy parts to be welded, so that the volume ratio of the brazing filler metal to the weld is 1.12;

[0040] Place the parts with brazing filler metal into the vacuum furnace and evacuate to 10 ～2 Pa;

[0041] Maintaining vacuum, the temperature was raised to 180°C at a rate of 2°C / s and kept at this temperature for 10 minutes;

[0042] Fill the furnace with nitrogen until the pressure inside the furnace reaches 35 kPa, raise the temperature to 262 °C at a rate of 1 °C / s, and keep it at that temperature for 6 minutes;

[0043] The temperature was raised to 350°C at a rate of 2°C / s and kept at that temperature for 30 seconds. After the holding period, the vacuum was immediately evacuated to below 10Pa, and then nitrogen was quickly filled and the temperature was lowered to 240°C at a rate of 1°C / s before being taken out of the furnace and air-cooled.

[0044] After welding is completed, the surface consistency is good, the airtightness test is qualified, the weld structure is dense, and there are no defects such as bubbles and voids.

[0045] In this technical solution:

[0046] Since this process is aimed at hole assembly welding, when calculating the volume ratio of solder and weld, the volume of the weld is obtained by subtracting the volume inside the hole from the volume of the part inserted into the hole, and then the volume of the filling solder is determined.

[0047] The volume ratio of solder to weld needs to be controlled between 0.85 and 1.25. When the volume ratio is less than 0.85, the solder will not be able to fill the weld, affecting the air tightness of the weld and easily causing weld voids. When the volume ratio is greater than 1.25, the solder will flow irregularly, affecting the appearance of the part.

[0048] The preheating temperature is increased at a rate of 1-2℃ / s to 150-180℃, and kept warm for 5-10 minutes. The shielding gas temperature is increased at a rate of 1-2℃ / s to 250-270℃, and kept warm for 1-5 minutes. The welding temperature is increased at a rate of 1-2℃ / s to 310-350℃, and kept warm for 30 seconds to 3 minutes. The cooling temperature is reduced at a rate of 1-2℃ / s to below 250℃ and then air-cooled. This step-by-step heating can ensure uniform heating of parts and solder. The cooling process starts with fast cooling and then slow cooling, which can refine the weld structure and reduce dendrite segregation. Slow cooling below the solidification point of the solder can eliminate internal stress and avoid welding cracks and raw material Si cracks.

Claims

1. A brazing process for high-silicon aluminum alloy hole assembly parts, comprising the following steps: s1. Material selection: Select silicon-aluminum alloy with silicon content of 30% to 70%, and Au80Sn20 eutectic solder; s2. Surface treatment: plating Ni-P layer and Au layer on the surface of silicon aluminum alloy parts in sequence; s3. Prepare the brazing filler metal: Prepare the brazing filler metal into the weld of the silicon-aluminum alloy parts to be welded, so that the volume ratio of the brazing filler metal to the weld is 0.85-1.25; s4. Place the parts with brazing filler metal into the vacuum furnace and evacuate to 10 ～2 Pa; s5. Maintaining vacuum, raise the temperature to 150-180°C at a rate of 1-2°C / s and keep warm for 5-10 minutes; s6. Fill the furnace with nitrogen until the pressure inside the furnace is between 30 and 90 kPa, and heat it to 250-270 °C at a rate of 1-2 °C / s, and keep it warm for 1-5 minutes; s7. Raise the temperature to 310-350℃ at a rate of 1-2℃ / s and keep warm for 30 seconds to 3 minutes. After the insulation is completed, immediately evacuate to below 10Pa, then quickly fill with nitrogen and cool to below 250℃ at a rate of 1-2℃ / s. Remove from the furnace and air cool.

2. A brazing process for high silicon aluminum alloy hole assembly according to claim 1, characterized in that: The Ni-P layer is formed by chemical plating, and the Au layer is formed by electroplating.

3. A brazing process for high silicon aluminum alloy hole assembly according to claim 1 or 2, characterized in that: The thickness of the Ni-P layer is 3 to 15 μm, and the thickness of the Au layer is 0.5 to 5 μm.

4. A brazing process for high silicon aluminum alloy hole assembly according to claim 1, characterized in that: The silicon-aluminum alloy parts and solder are ultrasonically cleaned in an anhydrous ethanol solution for 8 to 10 minutes before being loaded into the furnace, and then blown dry with nitrogen before the solder is prepared.