HIGH STRENGTH ALUMINUM ALLOY FIN STOCK FOR HEAT EXCHANGER

Abstract

The present invention provides an aluminum alloy fm stock alloy material with higher strength, and improved sag resistance for use in heat exchangers. This aluminum alloy fm stock alloy material was made by direct chill (DC) casting.

Description

FIELD OF THE INVENTION

The present invention relates to the fields of material science, material chemistry, metallurgy, aluminum alloys, aluminum fabrication, and related fields. The present invention provides novel aluminum alloys for use in the production of heat exchanger fins, which are, in turn, employed in various heat exchanger devices, for example, motor vehicle radiators, condensers, evaporators and related devices.

BACKGROUND

There is a need for aluminum alloy fin stock with high strength and improved sag resistance high strength for use in various heat exchanger applications including radiators for automobiles. There is a need to obtain aluminum alloy fin stock with strong pre-braze mechanical properties, good behavior during brazing, i.e., enhanced brazed material sag resistance and reduced fin erosion, and good strength and conductivity characteristics after braze for high performance heat exchanger applications.

SUMMARY

The present invention provides an aluminum alloy fin stock alloy material with higher strength, and improved sag resistance for use in heat exchangers. This aluminum alloy fin stock alloy material was made by direct chill (DC) casting.

A DC fin stock material was developed with desirable pre-braze (H14 temper) and post-braze mechanical properties, sag resistance, corrosion resistance and conductivity. The aluminum alloy fin stock alloy displays larger grain and improved strength before brazing.

The aluminum alloy fin stock alloy can be used in various applications, for example heat exchangers. The finstock is particularly useful for high performance light weight, automotive heat exchangers but could be used for other brazed applications including but not limited to HVAC. In one embodiment, the aluminum alloy fin stock alloy can be used in automotive heat exchangers such as radiators, condensers and evaporators. Other objects and advantages of the invention will be apparent from the following detailed description of embodiments of the invention.

DESCRIPTION

The present invention provides an aluminum alloy fin stock alloy material with higher strength, improved corrosion resistance and improved sag resistance for use in heat exchangers, such as automotive heat exchangers. This aluminum alloy fin stock alloy material was made by direct chill casting.

This DC fin stock material exhibits desirable pre-braze (H14 temper) and post-braze mechanical properties, sag resistance, corrosion resistance and conductivity. The aluminum alloy fin stock alloy displays larger grain and improved strength before brazing.

The aluminum alloy fin stock alloy can be used in various applications, for example heat exchangers. In one embodiment, the aluminum alloy fin stock alloy can be used in automotive heat exchangers such as radiators, condensers and evaporators.

In one embodiment, the DC fin stock material comprises about 0.8-1.4% Si, 0.4-0.8% Fe, 0.05-0.4% Cu, 1.2-1.7% Mn and 1.2-2.3% Zn, remainder aluminum. All % values are in weight (wt) %.

In another embodiment, the DC fin stock material comprises about 0.9-1.3% Si, 0.45-0.75% Fe, 0.10-0.30% Cu, 1.3-1.7% Mn and 1.30-2.2% Zn, remainder aluminum.

In yet another embodiment, the DC fin stock material comprises about 0.9-1.2% Si, 0.50-0.75% Fe, 0.15-0.30% Cu, 1.4-1.6% Mn and 1.4-2.1% Zn, remainder aluminum.

Optionally, Cr and/or Zr or other grain size controlling elements may be present in these alloy compositions up to 0.2% each, up to 0.15% %, up to 0.1%, up to 0.05%, or up to 0.03%. All % values are in weight (wt) %.

It is to be understood that the alloy compositions described herein may contain other minor elements sometimes referred to as unintentional elements, below 0.05%.

Method of Making the Ingots

The ingots described herein are made with a Direct Chill (DC) process, which is commonly used throughout the aluminum sheet industry, whereby a large ingot ˜1.5 m×0.6 m×4 m is cast from a large holding furnace which supplies metal to a shallow mold or molds supplied with cooling water. The solidifying ingot is continuously cooled by the direct impingement of the cooling water and is withdrawn slowly from the base of the mold until the full ingot or ingots are completed. Once cooled from the casting process, the ingot rolling surfaces are machined to remove surface segregation and irregularities. The machined ingot is preheated for hot rolling. The preheating temperature and duration are controlled to low levels to preserve a large grain size and high strength after the finished fin stock is brazed. The ingot is hot rolled to form a coil which is then cold rolled. The cold rolling process takes place in several steps and an interanneal in the range of about 300-450° C. is applied to recrystallize the material prior to the final cold rolling step. Next the material is cold rolled to obtain the desired final gauge and slit in narrow strips suitable for the manufacture of radiators and other automotive heat exchangers. A pre-heat of the ingots prior to hot rolling is conducted in such a way that the final metal temperature achieved is about 480° C. and is held there for an average of about 4 hours (typically a minimum of about 2 hours and a maximum of about 12 hours). Several ingots (about 8 to 30) are charged to a furnace and preheated with gas or electricity to the rolling temperature. Aluminum alloys are typically rolled in the range of about 450° C. to about 560° C. If the temperature is too cold, the roll loads are too high, and if the temperature is too hot, the metal may be too soft and break up in the mill. In this case the preheat temperature is low relative to other aluminum products and the hold time is relatively short, to limit the growth of dispersoids that would decrease the final post braze grain size. In practice a hot mill is scheduled to roll many different ingots and alloys and cannot always roll the ingots at minimum soak time. In one embodiment, the minimum soak time at about 480° C. is about 2 hours. During production, the inter-anneal temperature applied was about 400° C. for an average of about 3 hours followed by applying % cold work (CW) of about 29% to final gauge. The % CW is the degree of cold rolling applied to get the material in the final required strength range. The % cold work is defined as: (initial gauge−final gauge)*100/initial gauge. As cold work increases, the H14 strength increases, but final post braze grain size and sag resistance is decreased. 29% is relatively low for most aluminum rolling applications.

In one embodiment a pre heat practice at about 480° C. for an average of 4 hours is employed with an interanneal temperature of about 300-400° C. and % CW of about 25-35% to final gauge.

The finished cold rolled coil is then slit into many narrow strips of the width required by the heat exchanger manufacturer for forming, assembly and brazing into the finished heat exchanger.

The following example will serve to further illustrate the present invention without, at the same time, however, constituting any limitation thereof. On the contrary, it is to be clearly understood that resort may be had to various embodiments, modifications and equivalents thereof which, after reading the description herein, may suggest themselves to those skilled in the art without departing from the spirit of the invention.

EXAMPLE

A DC case alloy composition was made. The composition range of the alloy was within the following specification: 1.1±0.1% Si, 0.6±0.1% Fe, 0.2±0.05% Cu, 1.4±0.1% Mn and 1.50±0.1% Zn with the remainder aluminum. The alloy material had a minimum ultimate tensile strength of ˜130 MPa. The alloy material had an average conductivity after brazing of ˜43 IACS (International Annealed Copper Standard (i.e., pure copper is 100% conductivity)) and an open circuit potential corrosion value (vs. Standard Calomel Electrode (SCE)) of −741 mV. The alloy material produced exhibited a sag value between 28 mm where the final gauge was 49 μm, and 43 mm where the final gauge was 83 μm, which was within the required specifications at these gauges. These values were measured after applying a simulated brazing cycle whereby the sample was heated to a temperature of 605° C. and cooled to room temperature in a period of about 20 minutes to simulate the temperature time profile of a commercial brazing process. The alloy material produced varied in gauge between 49 and 83 μm.

All patents, patent applications, publications, and abstracts cited above are incorporated herein by reference in their entirety. Various embodiments of the invention have been described in fulfillment of the various objectives of the invention. It should be recognized that these embodiments are merely illustrative of the principles of the present invention. Numerous modifications and adaptations thereof will be readily apparent to those of skill in the art without departing from the spirit and scope of the invention as defined in the following claims.

Claims

1. An aluminum alloy comprising about 0.8-1.4 wt % Si, 0.4-0.8 wt % Fe, 0.05-0.4 wt % Cu, 1.2-1.7 wt % Mn and 1.20-2.3 wt % Zn with the remainder as Al.

2. The aluminum alloy of claim 1, comprising about 0.9-1.3 wt % Si, 0.45-0.75 wt % Fe, 0.10-0.3 wt % Cu, 1.3-1.7 wt % Mn and 1.30-2.2 wt % Zn, with the remainder as Al.

3. The aluminum alloy of claim 1, comprising about 0.9-1.2 wt % Si, 0.5-0.75 wt % Fe, 0.15-0.3 wt % Cu, 1.4-1.6 wt % Mn and 1.4-2.1 wt % Zn, with the remainder as Al.

4. The aluminum alloy of claim 1, further comprising up to 0.2 wt % of one or both of Cr or Zr.

5. An aluminum alloy fin stock material produced from the aluminum alloy of claim 1 by a process, comprising: direct chill casting the aluminum alloy into an ingot;preheating the ingot to 450 to 560° C. for 2 to 16 hours;hot rolling the preheated ingot;cold rolling the ingot;inter-annealing at a temperature of 300-450° C.; and,after inter-annealing, performing a final cold rolling step to achieve % cold work (%CW) of 25-35%.

6. The aluminum alloy fin stock material of claim 5, wherein the ingot is preheated at 480° C. for 2-12 hours.

7. The aluminum alloy fin stock material of claim 5, wherein the inter-annealing temperature is 300-400° C.

8. The aluminum alloy fin stock material of claim 5, having a minimum ultimate tensile strength of ˜130 MPa, measured after brazing.

9. The aluminum alloy fin stock material of claim 5, having a corrosion potential of −700 mV or less, measured after brazing.

10. A heat exchanger comprising the aluminum alloy of claim 1 or the aluminum alloy fin stock material of claim 5.

11. The heat exchanger of claim 10, wherein the heat exchanger is an automotive heat exchanger.

12. The heat exchanger of claim 10, wherein the heat exchanger is a radiator, a condenser or an evaporator.

13. Use of the aluminum alloy of claim 1 or the aluminum alloy fin stock material of claim 5 for fabrication of heat exchanger fins.

14. A process for making an aluminum alloy fin stock material, comprising: direct chill casting the aluminum alloy of claim 1 into an ingot;preheating the ingot to 450 to 560° C. for 2 to 16 hours;hot rolling the preheated ingot;cold rolling the ingot;inter-annealing at a temperature of 300-450° C.; and,after inter-annealing, performing a final cold rolling step to achieve % cold work (%CW) of 25-35%.

15. The process of claim 14, wherein the ingot is preheated at 480° C. for 2-12 hours.

16. The process of claim 14, wherein the inter-annealing temperature is 300-400° C.

17. The process of claim 15, wherein the inter-annealing temperature is 300-400° C.