ALUMINIUM ALOY, SEMI-MANUFACTURED PRODUCT, ESPECIALLY FOR MANUFACTURING BLOCK JOINTS, METHOD FOR MAKING SUCH A SEMI-MANUFACTURED PRODUCT AND RESPECTIVE BLOCK JOINT

Abstract

 The invention pertains to an aluminium alloy, especially for manufacturing block joints (10), in particular block joints (10) of a brazed, in particular CAB brazed, automotive heat exchanger. Moreover, the invention pertains to a semi-manufactured product, especially for manufacturing such block joints, as well as to a method for making such a semi-manufactured product and correspondingly manufactured block joints. To improve the hardness of such an aluminium alloy and of products formed from such an aluminium alloy, the aluminum alloy of the invention comprises:
- copper (Cu) in an amount of 0.3 to 1.5 % by weight;
- magnesium (Mg) in an amount of 0.25 to 1.0 % by weight, preferably 0.25 to 0.5 % by weight;
- silicium (Si) in an amount of 0.5 to 1.2 % by weight; and
- manganese (Mn) in an amount of 1.0 to 2.0 % by weight.

Description

[0001] The present invention pertains to an aluminium alloy, especially for manufacturing block joints, in particular block joints of a brazed automotive heat exchanger. Moreover, the invention pertains to a semi-manufactured product, especially for manufacturing such block joints, as well as to a method for making such a semi-manufactured product and correspondingly manufactured block joints.

[0002] In automotive air-conditioning systems block joints are used to connect various other components to a heat exchanger to transfer of fluid. The block joint is brazed to the heat exchanger, which is formed from aluminium alloys. Several brazing methods are known in the art, but usually the block joints are brazed to the heat exchanger by Controlled Atmosphere Brazing (CAB) using NOCOLOK^® flux. The block joint comprises, among others, threaded holes. By means of the threaded holes, other components may be screwed to the block joint. Therefore a certain strength and/or hardness of the material is required.

[0003] Current materials for block joints use the mechanism of Mg₂Si phase hardening by using the elements Si and Mg. The problem is that the use of Mg is limited to 0.5% when NOCOLOK^® flux is used in the CAB brazing process. Otherwise, bad brazing occurs and voids are created. In practical applications, not more than 0.4% Mg is used to avoid an excessive void level. These block joints have a hardness of 41 HBW (Brinell hardness).

[0004] JP 2014-125657 A teaches a composition comprising an Al-Si aluminium alloy brazing material on a surface of an Al-Mn series aluminium core material. The core material comprises 1.0 to 2.0 % by weight of manganese (Mn), 0.1 to 1.0 % by weight of copper (Cu), 0.3 to 1.0 % by weight of silicium and 0.1 to 0.5 % of magnesium (Mg). A cladding material is rolled to the core material. The composition is used in automotive heat exchangers and has an enhanced material strength as well as fatigue strength and hardness. However, recent developments in air-conditioning systems require block joints of further improved strength and/or hardness.

[0005] Another composition comprising an aluminium alloy core material is known from WO 2014/157116 A1. The core material comprises 0.3 to 1.0% by weight of silicium (Si), 0.6 to 2.0% by weight of manganese (Mn), 0.3, to 1.0% by weight of copper (Cu) and 0.15 to 0.5% by weight of magnesium (Mg), wherein the respective lower limit of each constituent is excluded.

[0006] Yet another composition is know from WO 2013/111904 A1, namely a highly corrosion-resistant aluminium alloy brazing sheet, which is provided with an aluminium alloy core material, an aluminium alloy brazing material which is clad to one surface of the core material, and an aluminium alloy sacrificial anode material, which is clad to the other surface of the core material. The core material comprises 0.05 to 1.2% by weight of silicium (Si), 0.05 to 1.0% by weight of iron (Fe), 0.05 to 1.2% by weight of copper (Cu), and 0.6 to 1.0% by weight of manganese (Mn).

[0007] However, the above aluminium alloys were conceived for a different purpose, e.g. rolled flat material. In particular, the usability for block joints, particularly block joints with a sufficient hardness after brazing is unknown.

[0008] Therefore, the problem to be solved by the invention is providing an aluminium alloy as well as a semi-manufactured product, a method for making such a semi-manufactured product, and correspondingly, manufactured block joints which have a hardness of 50 HBW or more even after CAB brazing.

[0009] To solve this problem, the aluminium alloy may comprise:

• copper (Cu) in an amount of 0.3% to 1.5% by weight, especially 0.5% to 1.0% by weight;
• magnesium (Mg) in an amount of 0.25% to 1.0% by weight, preferably 0.3% to 0.5% by weight;
• silicium (Si) in an amount of 0.5% to 1.2% by weight, especially 0.6% to 0.9%; and
• manganese (Mn) in an amount of 1.0 to 2.0 % by weight, especially 1.3% to 1.8%.

[0010] In the above no more than Mg of 0.5%, particularly no more than Mg of 0.4% by weight should be used if Nocolok flux is utilized; if Cesium (Cs) flux is utilized, up to 1.0 % by weight of Mg is considered possible.

[0011] According to the present disclosure, the hardness can be improved even further with an aluminium alloy comprising:

• copper (Cu) in an amount of 0.6% to 0.9% by weight;
• magnesium (Mg) in an amount of 0.35% to 0.4% by weight, especially 0.37% to 0.4% by weight;
• silicium (Si) in an amount of 0.7% to 0.9% by weight;
• manganese (Mn) in an amount of 1.4% to 1.7% by weight.

[0012] Tests have shown that particular advantageous manganese (Mn) ranges are > 1.4%, preferably 1.42% to 1.7% by weight, or even 1.44% to 1.7% of weight. According to particularly advantageous embodiments of the invention the hardness could be improved if the aluminium alloy comprises manganese (Mn) in an amount of 1.42% to 1.56% by weight. According to yet another advantageous embodiment the aluminium alloy comprised manganese (Mn) in an amount of 1.5% to 1.7% by weight, especially of 1.52% to 1.7% of weight.

[0013] According to yet another embodiment the aluminium alloy comprised silicium (Si) in an amount of 0.75% to 0.9% by weight, especially of 0.75% to 0.85% of weight.

[0014] The semi-manufactured product of the invention is obtained by extrusion of such an aluminium alloy. Accordingly, the method of the invention for making this semi-manufactured product comprises the steps of:

a) providing such an aluminium alloy; and

b) extruding the aluminium alloy.

[0015] The block joint according to the present invention is made from such a semi-manufactured product and/or obtained by such a method.

[0016] To find the process window of the invention, several tests and trials were performed. To increase hardness, Mn was added. A lower amount of Mn might decrease hardness, while a higher amount of Mn could make the processing of the material by extrusion, as it is intended, to obtain the semi-manufactured product, which is explained further below, more difficult, and it should be avoided due to process control reasons.

[0017] Also to increase hardness, Cu was added. However, Cu is a noble element. Calculation showed that the maximum Cu amount should not exceed 1%. Otherwise, the electrode potential gap in relation to the non-noble counterpart (Zn-cladded tank header of a heat exchanger) to which the block joint is brazed, would lead to a selective corrosion attack. Cu also makes the material very brittle during extrusion, so having too much Cu should be avoided since this could lead to hot tearing (overheating and cracking) during extrusion.

[0018] After the solidification of the aluminium alloy, dispersion phases consisting of Si with Mn and, as an unavoidable contaminant, Fe, are formed in the aluminium alloy. The above range of the Si amount used for the invention provides high Si for the Mg₂Si phase, which forms at lower temperatures. A higher Si limit might reduce the melting point, which should be avoided due to the brazing process; otherwise, partial melting could occur during brazing. At a lower Si range, it is very likely that the hardness would drop below 50 HBW after brazing.

[0019] After all, according to the invention, a hard matrix created by Cu, Mn and Mg is combined with a precipitation hardening from Mg and Si. Additionally, precipitations, e.g. Mg₂Si, give the material additional strength.

[0020] In general, aluminium alloys contain other unavoidable contaminants. To further improve the invention, these contaminants should not exceed the following limits:

• iron (Fe) not more than 0.6% by weight, especially not more than 0.4% by weight;
• zinc (Zn) not more than 0.8% by weight, especially not more than 0.1% by weight;
• chromium (Cr) not more than 0.3% by weight, especially not more than 0.05% by weight;
• titanium (Ti) not more than 0.2% by weight, especially not more than 0.08% by weight; and/or
• zirconium (Zr) not more than 0.15% by weight.

[0021] Fe is not only considered an unavoidable contaminant, but it is also beneficial to this invention. Therefore, the above limit is accepted to enable an economical production process, but 0.6% by weight, more favourably 0.4% by weight must not be exceeded to avoid negative effects of Fe in the matrix.

[0022] As mentioned above, the counterpart, to which the block joint is brazed, is often cladded with Zn on the surface. To avoid bad flow of the flux or a brazing fillet, that is excessively non-noble, due to the diffusion of Zn, the amount of Zn should not exceed 0.8 % by weight, more favourably 0.1 % by weight. However, a high content of an MgZn₂ phase could have beneficial effects, but too much Zn would be necessary to achieve these effects.

[0023] Zirconium poisons the grain refinement effect of TiB₂ in a direct chill ("DC") casting process and leads to a coarse grained microstructure with reduced strength and increased brittleness or to centre cracks in the as cast billet. Chromium increases the quench sensitivity after solution heat treatment and leads to decreased strength after artificial or natural ageing.

[0024] The semi-manufactured product, according to the invention, may be obtained by the extrusion process comprising:

• heating the aluminium alloy to a temperature of 450 °C to 550 °C;
• extruding the heated aluminium alloy with a speed of 4 m/min to 10 m/min.

[0025] A further improvement of the hardness, of the semi-manufactured product, may be achieved by homogenizing the aluminium alloy prior to the extrusion process. A homogenous Cu distribution achieved by the homogenisation process and extrusion process avoids intergranular corrosion, and thus provides good corrosion properties.

[0026] A key advantage is that a thus produced block joint has a hardness of 50 HBW or more immediately after brazing.

[0027] The block joint, according to the invention, is intended to be brazed to a counterpart, especially a heat exchanger. According to a further improvement of the invention, the block joint is naturally or artificially aged for at least 45 hours, preferably at least 48 hours, at 20 °C or higher, especially at 20 °C to 150 °C after brazing. It may happen that the hardness and/or strength of the material decreases initially after brazing. Aging allows the material to recover from this decrease. A thus aged material typically reaches a permanent hardness of 55 HBW or more.

[0028] Also it proved to be advantageous to conduct the brazing essentially in absence of bismuth (Bi).

[0029] Additional features and advantages of the invention will be more apparent from the following description of embodiments and accompanying drawings. The drawings show:

Fig. 1

a block joint comprising the features of the invention in an isometric view,

Fig. 2

the block joint of Fig. 1 in a bottom view,

Fig. 3

the block joint of Fig. 1 in a front view,

Fig. 4

the block joint of Fig. 1 in a left side view,

Fig. 5

a chart showing the natural aging of one embodiment of the invention at room temperature,

Fig. 6

a chart showing the artificial aging of one embodiment of the invention at a temperature of 150 °C, and

Fig. 7

a chart showing electrode potential characteristics of one embodiment of the invention.

[0030] Fig. 1 to 4 show a component integrally formed from an aluminium alloy according to the invention. In particular, a block joint 10 used in an automotive air-conditioning system is shown. The block joint 10 comprises a body 11 and a leg 12. The leg 12 serves to braze the block joint 10 to a counterpart, e.g. a heat exchanger (condenser) of the air-conditioning system. Brazing may be performed by CAB brazing with NOCOLOK^® flux.

[0031] The block joint 10 serves to support other components of the air-conditioning system, such as pipes or conduits. Therefore, the body 11 may comprise fastening and/or support means for fixing and/or supporting these components, such as one or more threaded holes 13, holes 14, threaded bolts or the like.

[0032] For the block joint 10, a hardness of 50 HBW is required. For automotive air-conditioning systems with CO₂ technology, a hardness of even 55 HBW is currently demanded by some system configurations. To achieve this hardness, the block joints 10 are manufactured as follows:

[0033] Firstly, an aluminium alloy is provided. In a first test, the aluminium alloy is specified to have the target composition and actually has the composition (Example 1) as indicated in the following table:

Element	Specification (% by weight)		Actual amount (% by weight)
	Lower limit	Upper limit	Example 1
Copper (Cu)	0.6	0.8	0.688
Magnesium (Mg)	0.35	0.40	0.36
Silicium (Si)	0.6	0.8	0.70
Manganese (Mn)	1.1	1.4	1.340
Iron (Fe)	0.2	0.4	0.32
Zinc (Zn)		0.1	0.013
Chromium (Cr)		0.05	0.005
Titanium (Ti)		0.08	0.024
Zirconium	0.11	0.15	0.11

[0034] The aluminium alloy may be cast to form billets and soaked. Besides billets, other preparations may be used if deemed appropriate.

[0035] Now, the aluminium alloy is harmonized by heating it at a temperature of 530 °C to 600 °C for 150 minutes to 480 minutes. Afterwards, it may be cut as deemed appropriate, and then, pre-heated to prepare it for the subsequent extrusion process. However, the aluminium alloy may be prepared for the extrusion process otherwise.

[0036] A semi-manufactured product is formed from the thus prepared aluminium alloy by an extrusion process at a temperature of 450 °C to 550 °C at a speed of 4 m/min to 10 m/min. The diameter and shape of the die is not specified and may be selected to fit the dimensions of the resulting product, i.e. the block joint 10. A controlled cooling from the extrusion temperature below 200 °C within 2 minutes may be applied in order to improve the result.

[0037] The thus formed semi-manufactured product is machined as appropriate to form the block joint into its final shape. In particular, a CNC (Computer Numerical Control) machining process is utilized. However, other forming processes are possible. For example, forging is considered as a forming process. Moreover, fastening means and/or supporting means such as threaded holes 13, holes 14 and/or threaded bolts are formed, e.g. cut.

[0038] The block joint 10 is now ready to be brazed to a heat exchanger. Brazing is performed by CAB brazing with NOCOLOK^® flux. Initially, this brazing process results in a decrease in hardness, but after a natural aging process of 3 days at 20 °C a hardness of around 55 HBW is reached. In the case of artificial aging at higher temperatures typically between 150 °C to 180 °C this process can be shortened.

[0039] To further improve the hardness of the block joint after brazing, the specification is set as shown by the table below. With this specification, two different test aluminium alloys (Example 2 and Example 3) are prepared having the actual composition as indicated in the table below as well. Favourable results were obtained especially with manganese (Mn) in an amount between 1.44% to 1.56% by weight, silicium (Si) in an amount between 0.75% and 0.85% and magnesium (Mg) in an amount between 0.37% and 0.40%.

Element	Specification (% by weight)		Actual amount (% by weight)
	Lower limit	Upper limit	Example 2	Example 3
Copper (Cu)	0.6	0.9	0.805	0.708
Magnesium (Mg)	0.35	0.40	0.39	0.37
Silicium (Si)	0.7	0.9	0.82	0.79
Manganese (Mn)	1.4	1.7	1.56	1.44
Iron (Fe)		0.4	0.4	0.31
Zinc (Zn)		0.1	0.02	0.026
Chromium (Cr)		0.05	0.014	0.012
Titanium (Ti)		0.08	0.02	0.018
Zirconium		0,05	0.01	0.01

[0040] The thus prepared aluminium alloy is further processed as explained for example 1 above.

[0041] After brazing and then natural aging at 20°C of the block joint, a hardness of 58 HBW is achieved with Example 2, and 59 HBW with Example 3 after approximately 48 hours upon brazing.

[0042] Fig. 5 shows a chart depicting the aging of the brazed block joint at room temperature for Example 2. Before the brazing, the hardness is almost 65 HBW, but after brazing the hardness initially drops to 50 HBW. After 3 days, the hardness is back at 55 HBW and, hence, meets the requirement for use with CO₂ technology. After 8 days, the hardness is about to saturate at almost 60 HBW.

[0043] Fig. 6 shows a chart depicting the aging of the brazed block joint at 150 °C for Example 1. After brazing, the hardness initially is slightly below 55 HBW. After about 100 hours, the hardness reaches its maximum at about 83 HBW. During further aging, the hardness decreases slightly but saturates at about 81 HBW.

[0044] Moreover, Fig. 6 depicts the development of the yield strength Rp0.2, and the tensile strength Rm during the aging process.

[0045] Fig. 7 is a chart depicting the electrode potential of all three examples versus time at a temperature of 165 °C (operating temperature of the block joint in C0₂ technology). All three examples have proven to show excellent high-temperature properties. The electrode potential is similar to current material. Therefore, no corrosion potential exists to create cathodic corrosion.

Claims

1. Aluminium alloy, especially for manufacturing block joints (10), in particular block joints (10) of a brazed, in particular CAB brazed, automotive heat exchanger, the aluminium alloy comprising:

- copper (Cu) in an amount of 0.6% to 0.9% by weight;

- magnesium (Mg) in an amount of 0.35% to 0.4% by weight, especially 0,37 % to 0,4 % by weight;

- silicium (Si) in an amount of 0.7% to 0.9% by weight; and

- manganese (Mn) in an amount of 1.4% to 1.7% by weight.

2. Aluminium alloy of claim 1, comprising Manganese (Mn) in an amount of 1.42% to 1.7% by weight, especially of 1.44% to 1.7% of weight.

3. Aluminium alloy of claim 2, comprising Manganese (Mn) in an amount of 1.42% to 1.56% by weight.

4. Aluminium alloy of claim 2, comprising Manganese (Mn) in an amount of 1.5% to 1.7% by weight, especially of 1.52% to 1.7% of weight.

5. Aluminium alloy of any one of the preceding claims, comprising silicium (Si) in an amount of 0.75% to 0.9% by weight, especially of 0.75% to 0.85% of weight.

6. Aluminium alloy of any one of the preceding claims, further comprising:

- iron (Fe) in an amount of not more than 0.6% by weight, especially not more than 0.4% by weight; and/or

- zinc (Zn) in an amount of not more than 0.8% by weight, especially not more than 0.1% by weight; and/or

- chromium (Cr) in an amount of not more than 0.3% by weight, especially not more than 0.05% by weight; and/or

- titanium (Ti) in an amount of not more than 0.2% by weight, especially not more than 0.08% by weight; and/or

- zirconium (Zr) in an amount of not more than 0.15% by weight.

7. Semi-manufactured product, especially for manufacturing block joints (10), in particular block joints (10) of a brazed automotive heat exchanger, obtained by extrusion of the aluminium alloy of any one of claims 1 to 6.

8. Semi-manufactured product of claim 7, wherein the extrusion process comprises:

- heating the aluminium alloy to a temperature of 450 °C to 550 °C;

- extruding the heated aluminium alloy with a speed of 4 m/min to 10 m/min.

9. Semi-manufactured product of claim 7 or 8, wherein the aluminium alloy is homogenized prior to the extrusion process.

10. Method for making a semi-manufactured product, especially for manufacturing block joints (10), in particular block joints (10) of a brazed automotive heat exchanger, comprising the steps of:

a) providing an aluminium alloy of any one of claims 1 to 6; and

b) extruding the aluminium alloy.

11. Method of claim 10, wherein the extrusion process comprises the steps of:

- heating the aluminium alloy to a temperature of 450 °C to 550 °C;

- extruding the heated aluminium alloy with a speed of 4 m/min to 10 m/min.

12. Method of claims 10 to 11, wherein the aluminium alloy is homogenized prior to the extrusion process.

13. Block joint (10), in particular block joint (10) of a brazed automotive heat exchanger, made from the semi-manufactured product of any one of claims 7 to 9 and/or obtained by the method of any one of claims 10 to 12.

14. Assembly comprising the block joint (10) of claim 13 and a counterpart, especially a heat exchanger, to which the block joint (10) is brazed, wherein the block joint (10) is naturally or artificially aged for at least 45 hours, preferably 48 hours, at 20 °C or higher, especially at 20 °C to 150 °C, preferably 20 °C to 180 °C, after brazing.

15. Method of claim 14, wherein the brazing is done according to a controlled atmosphere Brazing (CAB), preferably with a flux medium and/or essentially without the presence of bismuth (Bi).

Drawing