RU2596535C2 - Solder for soldering aluminium and alloys thereof - Google Patents

Abstract

FIELD: metal processing.

SUBSTANCE: invention can be used in producing soldered structures from aluminium and its alloys. Solder contains components in following ratio, wt%: silicon 5-13, copper 1-13.5, zinc 2-10, nickel 0.5-4.5, tin 0.1-0.3, at least one element from a group comprising strontium 0.001-0.2, sodium 0.001-0.2, titanium 0.001-0.1, vanadium 0.001-0.2, at least one element selected from a group of cobalt 0.001-0.8, molybdenum 0.001-0.8; beryllium 0.001-0.1, aluminium - balance. Total content of zinc and copper is not more than 15 wt%, ratio of nickel content to copper ranges from 1:2 to 1:4. During vacuum soldering solder additionally contains magnesium in amount of 0.1-1 wt%.

EFFECT: solder provides high level of strength of soldered joint with possibility of conducting process of soldering at temperatures below 590 °C, which enables to use in soldered structures of most modern structural aluminium alloys.

1 cl, 2 tbl, 3 ex

Description

The invention relates to the field of metallurgy and can be used to obtain soldered structures from aluminum and its alloys.

Known solder composition (wt.%): Copper 15-30, zinc 15-30, silicon 1-10, aluminum - the rest (JP No. 2001062587, IPC B23K 35/28, C22C 21/00, 2001). The disadvantages of the solder are the low technological ductility and corrosion resistance of soldered joints due to the high content of copper and zinc.

Known solder composition (wt.%): Silicon 5-13, zinc 1-5, copper 2-6, nickel 0.5-5, at least one of the elements: strontium 0.02-0.2, barium 0 , 05-0.3, antimony 0.05-0.3, aluminum - the rest (JP No. 2000096168), adopted as a prototype. The disadvantages of the solder are the low processability during soldering due to the high melting point, including the tendency to microcracks during crystallization.

The objective of the invention is to improve manufacturability during soldering, strength, and corrosion resistance of soldered joints.

The technical result consists in lowering the melting point of the solder, improving technological properties during soldering, increasing the strength and corrosion resistance of soldered joints.

The technical result is achieved in that the solder for brazing aluminum and its alloys, containing silicon, zinc, copper, nickel, aluminum, additionally contains tin, at least one element from the group: strontium, sodium, titanium, vanadium, and at least one an element from the group: cobalt, molybdenum, beryllium, in the following ratio of components (wt.%):

silicon 5-13 zinc 2-10 copper 1-13.5 nickel 0.5-4.5 tin 0.1-0.3

at least one element from the group:

strontium 0.001-0.2 sodium 0.001-0.2 titanium 0.001-0.1 vanadium 0.001-0.2

at least one element from the group:

cobalt 0.001-0.8 molybdenum 0.001-0.8 beryllium 0.001-0.1 rest aluminum

moreover, the total content of zinc and copper does not exceed 15 wt.%, and the ratio of the content of Nickel to copper is from 1: 2 to 1: 4.

When vacuum soldering, the solder additionally contains magnesium in an amount of 0.1-1 wt.%.

The main alloying components of the solder are silicon, copper and zinc, which provide a decrease in its melting point.

Silicon forms an eutectic Al-12Si (wt.%) With aluminum with a melting point of 577 ° C. The lower silicon content of 5% in the proposed solder is determined by the conditions of sufficient fluidity and prevent the formation of hot cracks during soldering. An upper silicon content of 13% allows a significant part of the solder to crystallize near the eutectic “site”, only the low-melting phases (eutectics involving copper and zinc) remain liquid. At this point, the solder allows you to form a fairly strong structure that can withstand shrinkage until it completely hardens without the formation of hot cracks.

Copper and zinc contribute to lowering the melting point of solder.

To a greater extent, copper affects the melting temperature. However, due to the large difference in the standard electrode potentials, compared with the aluminum base, copper can significantly reduce corrosion properties. For this reason, to ensure satisfactory corrosion resistance of soldered joints, the copper content in the solder is limited to 13.5 wt.%.

Additional alloying with zinc also reduces the melting point of the solder, but to a lesser extent affects the corrosion properties of the solder joint. However, when the content in the zinc alloy is more than 10 wt.%, The strength characteristics of the latter decrease, which is due to the limitation of its content.

To ensure high mechanical and satisfactory corrosion properties of the brazed joints and to prevent the formation of hot cracks during brazing, the total content of copper and zinc in the alloy should not exceed 15 wt.%.

Small tin additives are used to modify the structure of the solder. To obtain the optimal structure, finely dispersed interdendritic distribution of tin is necessary. The solubility of tin in aluminum and zinc is extremely small (0.05-0.06 wt.%), The mutual solubility of tin and silicon is absent. The maximum tin content in the solder is limited to 0.3 wt.%, Because with a higher content, tin-containing phases may appear on the basis of low-melting eutectics such as Al-Sn (228.3 ° C), Al-Zn (198.5 ° C), Al-Si (232 ° C), which reduce corrosion resistance solder. When the tin content is less than 0.1% (wt.), The modifying effect of tin is not manifested.

Nickel is practically insoluble in aluminum, forming the NiAl ₃ phase and contributing to the strengthening of cohesive bonds, which is manifested when the content is above 0.5 wt.%. It is unlimitedly soluble in copper and in a fairly wide range of concentrations - in silicon, increasing their strength properties. When the content of nickel and copper in the solder of the claimed composition in a ratio of 1: 2 to 1: 4, nickel is almost completely present in phases based on copper and silicon. When the nickel content is more than 4.5% (mass.) And the ratio of nickel to copper is greater than 1: 2, an NiAl ₃ phase is formed in excess, which reduces the ductility of the solder. When the ratio Ni / Cu <1: 2, hardening is not effective. At the same time, the presence of nickel allows one to bind iron impurities, which are always present in aluminum alloys and reduce technological plasticity due to the transformation of phases of the Fe _m Al _n type into the Al ₉ FeNi phase, the effect of which is less negative.

Additives of titanium, sodium, strontium, vanadium serve as modifiers.

Strontium and sodium grind eutectic silicon precipitates and increase ductility and technological properties during rolling of solder. Typically, 0.001-0.2% strontium and / or sodium is introduced into eutectic silumins.

Titanium and vanadium in an amount of 0.01-0.3 wt.% Is introduced for grinding grain si-solid solution based on aluminum. The lower limit of the content (0.001 wt.%) Is due to the onset of the modification effect, the upper (titanium 0.1, vanadium 0.2 wt.%) Due to the formation of coarse phase particles that reduce the hardening effect.

The microadditive of beryllium in an amount of 0.001-0.1 wt.%, Due to the exceptional affinity of beryllium to oxygen, protects the molten solder from oxidation. According to some sources, beryllium can also have a modifying effect.

It is possible to alloy the solder with one modifier component, as well as a complex alloying that enhances the effect with several modifiers.

Additives of cobalt and molybdenum improve hardenability by slowing down the decomposition of the α-solid solution based on aluminum and stabilizing it at high temperatures. As a result, with soldering methods characterized by a long thermal cycle (cooling with a furnace, gas soldering), these components can slow down the decomposition of the solid solution and increase the mechanical properties of the metal of the brazed joint. Based on the extremely limited solubility of these components in aluminum, their content should not exceed 0.8 wt.%. With a higher content, cobalt and molybdenum form coarse intermetallic phases with other solder components. When the content is in an amount less than 0.001 wt.%, They do not significantly affect the properties of the compounds. The best properties of soldered joints are provided when the content of one or both components in the amount of 0.25-0.5 wt.%.

Magnesium is used as a metal activator to loosen and remove oxide film from the surface of the base metal and improve the wettability of the base metal with solder during flux-free brazing of aluminum alloys in vacuum. The activator metal, interacting with oxides, loosens them, which ensures access of liquid solder to the surface of the base metal. Additives of magnesium in an amount of 0.1-1 wt.% Are necessary and sufficient to obtain high-quality soldered joints.

Case Studies

Solders of the five proposed compositions (table 1) were obtained by melting AK12 ingots (Al-12Si) and dissolving nickel, copper, zinc, tin, cobalt and ligatures of strontium, vanadium, beryllium, titanium, and sodium in the melt.

For comparative tests, a prototype solder composition 6 was used (see table 1).

Soldered joints were subjected to mechanical tensile tests and tests for general corrosion in salt fog using an accelerated procedure.

Example 1. Ingots of the three proposed compositions 1-3 and prototype 6 (see table 1) were cast into a cooled mold in a semi-continuous way, cut into billets, which were subjected to hot and cold rolling to a thickness of 0.3-1.0 mm

The lapping of samples from alloy 1915 with solders of composition 1-3 using flux FPA-1 was carried out in a furnace with an air atmosphere. The temperature of soldering with solders of composition 1-3 was 575-580 ° C, solder-prototype of composition 6 was 580-585 ° C, the exposure time was 10 minutes. When soldering with a prototype solder, a lesser spreadability of the solder was noted compared with the declared one. Tensile tests (table 2), established that the claimed solder can increase the strength of the joints compared with the prototype by at least 18%. During the destruction at the seam of samples soldered by the prototype, defects were identified due to insufficient wettability of the base metal, the spreadability of solder and microcracks.

After corrosion testing of joints soldered by solders of composition 1-3, no traces of corrosion were detected, on the surface of the joints brazed by the prototype, local foci of corrosion damage occurred.

Example 2. Solder composition 4 (see table 1) from the crucible was poured onto a massive steel disk to obtain a "noodle" with a section of ≈3 × 4 mm. For comparative tests, "noodles" from a sheet of prototype solder 3-5 mm wide with a thickness of 3 mm were cut on guillotine shears.

The batch of lapping samples from alloy 1915 was soldered using a gas burner using flux Ф34А. Heating was carried out until the solder was completely melted, cooling was carried out in air.

After washing the samples from the flux residues, tensile tests were performed (see table 2). The average value of the strength of the joints brazed by the declared solder was 194 MPa. The destruction of the samples occurred on the base material. The average tensile strength of samples brazed with a prototype solder was 168 MPa, which is 15% less. The destruction of more than half of the samples occurred along a soldered seam.

After testing the corrosion resistance of samples soldered by a prototype solder, local foci of corrosion damage in the form of small white spots were identified on the surface of the soldered seam. On the surface of the samples soldered by the claimed solder, no foci of corrosion damage were visually detected.

Example 3. Ingot solders of the claimed composition 5 and prototype composition 6 (see table 1) were cast into a cooled mold in a semi-continuous manner, cut into billets that were hot and cold rolled to a thickness of 0.3-1.0 mm.

Lap joints from AD31 alloy were soldered in a SGV-2 vacuum furnace at a residual pressure in the chamber of 10 Pa. The soldering temperature of the claimed solder was 575-580 ° C, prototype solder - 580-585 ° C. The exposure at the soldering temperature for both solders was 2 min.

A visual inspection after soldering showed that the samples brazed by the prototype solder did not have smooth and continuous fillets; in some areas, remains of an unmelted solder in the form of a foil with a dark coating were observed. Therefore, the tests were carried out only on samples obtained using the claimed solder. It was established (see table 2) that the average tensile strength of the samples is 189 MPa (close to the strength values in examples 1-4). The destruction of the samples occurred on the base material. Accelerated corrosion tests showed satisfactory corrosion resistance of soldered joints.

Thus, the claimed solder provides higher strength (not lower than 170 MPa), corrosion resistance of solder joints and manufacturability of the solder, provides soldering at temperatures from 570 ° C, which will allow the use of solder for brazing most structural aluminum alloys.

Claims (2)

1. Solder for brazing aluminum and its alloys, containing silicon, zinc, copper, nickel, aluminum, characterized in that it further comprises tin, at least one element from the group: strontium, sodium, titanium, vanadium, and at least one element from the group: cobalt, molybdenum, beryllium, in the following ratio of components, wt.%:
silicon 5-13 zinc 2-10 copper 1-13.5 nickel 0.5-4.5 tin 0.1-0.3 strontium 0.001-0.2 sodium 0.001-0.2 titanium 0.001-0.1 vanadium 0.001-0.2 cobalt 0.001-0.8 molybdenum 0.001-0.8 beryllium 0.001-0.1 aluminum rest
moreover, the total content of zinc and copper does not exceed 15 wt.%, and the ratio of the content of Nickel to copper is from 1: 2 to 1: 4. 2. Solder according to claim 1. characterized in that it additionally contains magnesium in an amount of 0.1-1 wt.%.