JPS62164859A - Process for improving relative strength and breaking toughness of aluminum alloy containing lithium - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an aluminum alloy containing lithium as an alloying element, and more particularly to a busses for improving the fracture toughness of an aluminum-lithium alloy without reducing its strength.

BACKGROUND OF THE INVENTION Current large commercial transport airplanes produce 15 to 20 gallons (1 gallon - 3.8 g) per year for every 1 bond (approximately 453 grams, hereinafter the same) that is reduced in weight during the construction of the airplane. (similar) is estimated to save fuel. Over the airplane's design life of 20 years, this fuel savings amounts to 300 to 400 gallons. At current fuel costs, it makes sense to invest in reducing the weight of an airplane's structure in order to improve the overall economic efficiency of the airplane.

Improving performance in various types of airplanes requires the use of improved engines, improved airplane frame designs, or the use of new or improved structural materials. is necessary. Improvements in engine and airplane design have been vigorously pursued.

However, it is only recently that the development of new and improved structural materials has received considerable attention, and the employment of these materials in new airplane designs is expected to yield significant performance benefits. .

Materials have always played an important role when conceptualizing airplane structures. Since the early 1930s, the structural feed for large airplanes has been consistent, with aluminum being the basic structural material in wings, bodies, and tails, and steel for landing gear and other specialized materials characterized by particularly high strength. used in parts. However, over the past few years, several important new materials have been developed for use in aircraft construction. These materials include new metal materials, metal matrix composite materials, and resin matrix composite materials. Many believe that improved aluminum alloys and resin matrix carbon fiber materials will become the dominant aircraft structural materials in the coming decades. Although 1U composite materials will be increasingly used as aircraft structural materials, new lightweight aluminum alloys, especially aluminum lithium alloys, are highly desirable to expand the applications of this type of material. .

To date, aluminum-lithium alloys have only been used to a limited extent in aircraft construction. This low usage is due to the fact that compared to other conventional aluminum alloys, lithium-containing aluminum alloys are difficult to cast and have relatively low fracture toughness. However, the addition of lithium to aluminum results in a substantial reduction in density, which proves to be very important in reducing the overall weight of the aircraft structure. Although substantial progress has been made in improving processing techniques for aluminum-lithium alloys, obtaining a good combination of fracture toughness and high strength in this alloy remains a major research challenge.

SUMMARY OF THE INVENTION The present invention provides a method for aging aluminum-lithium alloys of various compositions at relatively low temperatures to provide improved and high fracture toughness without reducing strength. After the alloy is formed into an article, solution heat treated, and hardened, it is simply aged at a relatively low temperature for a relatively long period of time. This process is commonly referred to as low temperature underaging. More specifically,
The alloy is aged at temperatures ranging from 200°F to 300°F or less for times ranging from 1 hour to over 80 hours. This low-temperature aging treatment causes the alloy to have greater fracture toughness than traditional high-temperature aged materials, often on the order of 150-200%, while the strength remains comparable. .

DESCRIPTION OF THE EMBODIMENTS The aluminum-lithium alloy according to the present invention has a
Contains 3.2% lithium. According to current data,
The benefits of low temperature underaging are most evident at levels of lithium below 2.7%.

In this specification, percentages are by weight based on the total weight of the alloy, unless otherwise specified. Additional alloying elements such as magnesium, copper, and manganese may be added to the alloy. Additions of these alloying elements serve to improve general mechanical properties, but also affect density somewhat.

These alloys contain 0,
Zirconium is present at a level of 0.08-0.15%.

Zirconium is important for the development of desirable combinations of mechanical properties in aluminum-lithium alloys and is also important for our low temperature under-aged alloys.

The impurity elements iron and silicon are 0°3% and 0, respectively.
．． It may be present in amounts up to 5%. However, it is desirable that these elements be present in trace amounts of 0.10% or less. Trace elements such as zinc and titanium are each 0.2
Up to two not more than 5% and 0.1596 may be present.

Other trace elements such as cadmium and chromium must each be maintained at levels below 0.0596. If these maximum amounts are exceeded, the desired properties of the aluminum-lithium alloy will tend to deteriorate. The trace elements sodium and hydrogen are also considered to be detrimental to the properties of aluminum-lithium alloys and should be kept at the lowest practical levels, e.g. sodium at a maximum of 15-30 ppm.
(0,0015 to 0,003 (HI?, 12%), and for hydrogen 15p1) m(0,00
15% by weight) or less, preferably 1.0 ppm
(0,0001 weight 96) or less is desirable.

Of course, the remainder of the alloy consists of aluminum.

The following table shows the proportions in which alloying elements and trace elements may be present. The widest range is 6-effective under some circumstances, with the more preferred range offering a better blend of fracture toughness and strength. The most preferred range currently provides the best overall combination of properties for use in aircraft construction.

(Left below) Element Amount (weight 96) Li
1.0~3.2 1.5~3.0
1.8-2.7Mg 0-5.5.5
0~4.2 0~3.2Cu
0-5.4. 5 0-3. 7
0. 5-3. OZr 0. 0
8-0. 15 0. 08-0. 15 0.08~
0.15Mn 0-5.1. 2
0~0. 8 0-0. 6Fe
Maximum 0. 3 Maximum 0.15 Maximum 0.10Si Maximum 0.5 Maximum 0
．． 12 Maximum 0.10Zn Maximum 0,2
5 Maximum 0.10 Maximum 0.10Ti
Maximum 0.15 Maximum 0.10 Maximum 0.1ONa Maximum 0.0030 Maximum 0
．． 0015 Maximum 0.0015H Maximum 0.0015
Maximum 010005 Maximum o, oooi each trace element Maximum 0.05 Maximum 0.05 Maximum 0
．． 05 Total trace elements Maximum 0.25 Maximum 0.25
Maximum 0.25Al remaining amount
Remaining Amount The aluminum-lithium alloy prepared in the proportions indicated by the foregoing description and table is formed into the shape of an article by well known techniques. The alloy is prepared in liquid form and cast into ingots. The ingot is then homogenized at a temperature ranging from 925°F to about 1000°F. Thereafter, the alloy is converted into a useful article by conventional mechanical forming techniques such as rolling or extrusion. Once formed into an article, the alloy typically has a 950
Solution heat treated at temperatures ranging from °F to 1010 °F;
It is then quenched in a medium such as water maintained at a temperature on the order of 70°F to 150°F. If the alloy is rolled or extruded, it is usually 1 to 3 times the original length to relieve internal stresses and improve mechanical properties.
Stretched on the order of %. The aluminum alloy may then be processed and formed into various shapes for final use. At that time, if necessary, heat treatment as described above may be additionally employed.

Thereafter, according to the invention, the article is aged;
This increases the strength of the abrasive while maintaining fracture toughness and keeping other mechanical properties at relatively high levels. According to the present invention, the article can be heated from about 200°F to
Low temperature underage heat treatment at temperatures ranging down to 0°F and below. Considering the economic implications of minimizing the time consumed in commercial heat treatment equipment, from about 250'F to about 27.
Low temperature aging at temperatures in the range up to 5° F. is believed to be preferred for most alloys. At higher temperatures, less time will be required to achieve the proper match between strength and fracture toughness, but the overall property combination will be slightly worse. For example, 2
When aged at temperatures on the order of 75°F to just below 300°F, it is desirable that the product be held at the aging temperature for between 1 and 40 hours. On the other hand, when aged at temperatures on the order of 250 degrees Fahrenheit or less, aging times of 2 hours up to 80 hours or more are desirable to provide the proper balance between fracture toughness and strength. After aging, the aluminum-lithium product is cooled to room temperature.

When subjected to low temperature aging according to the parameters mentioned above, aluminum-lithium alloys typically have a temperature of 45 to 95 ksi (lks i=0
．． It has an ultimate strength on the order of 70 kg/mm2). The fracture toughness of the alloy is greater, often on the order of 1.5 to 2 times, than similar aluminum-lithium alloys aged to comparable strength levels by conventional aging treatments at temperatures above 300 degrees Fahrenheit.

The following examples are presented to illustrate the superior combination of strength and toughness obtained by low temperature underaging of aluminum-lithium alloys according to the present invention, and to assist those skilled in the art in making use of the present invention. It will be done. The following examples are not intended to limit the scope of this disclosure or the scope of post-patent protection in any way.

Fuel: 2.4% lithium, 1% magnesium, 1.3?6 copper,
An aluminum alloy was prepared containing 0.1596 zirconium and the remainder being aluminum.

The total trace elements present in the preparation were 0°25
It was 96 or less. Less than 0.07% of iron and silicon were each present in the preparation. The alloy was cast and homogenized at 975'F.

After that, the alloy is 0. 2 inches (1 inch - 2゜54
It was warm-rolled to a thickness of cm, hereinafter the same).

The resulting sheet was then conditioned at 795'F for approximately 1 hour. The sheet was then quenched in water maintained at about 70°F. After that, the sheet is 1.5 of the optimum length.
% and then cut into coupons. Some specimens were 0.5" x 2.5" x 2.5" for notched Charpy impact testing, a well-known method of measuring fracture toughness
Cut to 0.2 inch size. Other specimens prepared for tensile strength testing were 1 inch by 4 inches by 0.2 inches. The specimens were then heated at 350'F for 2
aged for 8 hours, 8 hours, and 16 hours; aged for 8 hours, 16 hours, and 48 hours at 325°F;
05°F for 8 hours; 275°F for 16 and 40 hours; and 250°F for 40 and 72 hours. Specimens aged at each temperature and time were subjected to notched Charpy impact tests and tensile strength tests according to standard test procedures. The test values of multiple samples aged at specific temperatures and times were averaged. These average test values are shown graphically in the figure. The numbers at each /1111 fixed point in the figure represent the aging time.

Referring to the figure, coupons aged at temperatures above 300°F have a rating of 225-52 as measured by the Charpy impact test.
5 inches-psi (psi-0゜07kg/cm2)
The toughness was on the order of . In contrast, specimens cured at low temperatures in accordance with the present invention exhibited toughness in the Charpy impact test on the order of 650 to almost 850 inches psi. Then, the average strength of those materials is
With the exception of coupons aged at 350'F for 16 hours, the yield fell within the range of 64-71 ksi. (However, 3
Specimens aged at 50'F showed lower toughness than any other specimens; i.e., according to the test results, specimens aged at 300'F
Relatively long aging at temperatures below 325~3
It is clear that this provides a combination of strength and toughness that is superior to specimens aged by conventional procedures at temperatures on the order of 50° F. for relatively short periods of time. The test results also show that when the aging temperature is lowered below 300'F, a significant improvement in the combination of strength and toughness properties results, i.e., higher fracture toughness for a given strength level. You can see what you can get.

The invention has been described in the context of various embodiments, including preferred processing parameters and preparations.

After reading this specification, those skilled in the art will be able to make various changes, sensible substitutions, and other modifications without departing from the broad concepts disclosed herein. For example, this low-temperature underaging treatment is also suitable for combinations of other alloying elements that are not currently under development, and specifically for significant amounts of alloying elements.
11 (lead, silicon, iron, nickel, beryllium, bismuth, germanium.

It can be applied to aluminum-lithium alloys including synechonium and synechonium. Therefore, it is intended that the scope of the patent application herein be limited only by the scope of the following claims or their equivalents.

[Brief explanation of drawings]

The figure is a graph showing the combination of fracture toughness and strength in several coupons of aluminum-lithium alloy aged at various times and degrees of crystallinity as mentioned in the examples. Patent applicant Kube Fukami, patent attorney representing The Boeing Company, '-1, I (2 idiots) Be1 Tomi-

Claims (6)

[Claims] (1) A process for improving the relative strength and fracture toughness of an aluminum alloy containing lithium as an alloying element, the alloy comprising: ￥Element￥￥Amount (wt%)￥Li 1.0 to 3.2 Mg 0-5.5 Cu 0-4.5 Zr 0.08-0.15 Mn 0-1.2 Fe max. 0.3 Si max. 0.5 Zn max. 0.25 Ti max. 0.15 Each trace element max. having a composition of 0.05 total trace elements and a maximum of 0.25 Al residual, said alloy is first formed in the form of an article;
solution heat treated and quenched, the process lasting about 20 hours for a period ranging from about 1 hour to more than 80 hours.
0°F to 300°F (in this specification, F=(9
/5) A process characterized in that it comprises the step of aging said alloy at a temperature in the range of C+32) or less. 2. The process of claim 1, wherein said aging temperature is less than or equal to about 275 degrees Fahrenheit. 3. The process of claim 1, wherein said aging temperature is from about 250°F to about 275°F. 4. The process of claim 1, wherein said aging temperature is less than or equal to about 250 degrees Fahrenheit. (5) The alloy is as follows: ￥Element￥￥￥￥(wt%)￥ Li 1.0-3.0 Mg 0-4.2 Cu 0-3.7 Zr 0.08-0.15 Mn 0-0.8 Claims characterized in that the composition has the following compositions: Fe max. 0.15 Si max. 0.12 Zn max. 0.10 Ti max. 0.10 Each trace element max. 0.05 All trace elements max. 0.25 Al Residual amount The process described in paragraph 1. (6) The above alloy includes: ￥Element￥￥￥Amount (weight%)￥ Li 1.8-2.7 Mg 0-3.2 Cu 0.5-3.0 Zr 0.08-0.15 Mn 0- 0.6 Fe max. 0.10 Si max. 0.10 Zn max. 0.10 Ti max. 0.10 Each trace element max. 0.05 All trace elements max. 0.25 Al A patent characterized by having a composition of max. A process according to claim 5.