Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C21/00—Alloys based on aluminium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/04—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon

Definitions

• the invention relates to aluminum alloys containing lithium as an alloying element, and particularly to a process for improving the fracture toughness of aluminum-lithium alloys without detracting from their strength.
• the present invention provides a method for aging aluminum-­lithium alloys of various compositions at relatively low temperatures to develop a high and improved fracture toughness without reducing the strength of the alloy.
• the alloy is aged at a relatively low temperature for a relatively long time.
• This process may be generally referred to as low temperature underaging.
• the alloy can be aged at temperatures ranging from 200°F to below 300°F for a period of time ranging from 1 up to 80 or more hours.
• This low temperature aging regimen will result in an alloy having a greater fracture toughness, often on the order of 150 to 200 percent, than that of materials aged at conventional higher temperatures while maintaining an equivalent strength.
• the impurity elements iron and silicon can be present in amounts up to 0.3 and 0.5 percent, respectively. It is preferred, however, that these elements be present only in trace amounts of less than 0.10 percent. Certain trace elements such as zinc and titanium may be present in amounts up to but not to exceed 0.25 percent and 0.15 percent, respectively. Certain other trace elements such as cadmium and chromium must each be held to levels of 0.05 percent or less. If these maximums are exceeded, the desired properties of the aluminum-lithium alloy will tend to deteriorate.
• An aluminum alloy containing 2.4 percent lithium, 1 percent magnesium, 1.3 percent copper, 0.15 percent zirconium with the balance being aluminum was formulated.
• the trace elements present in the formulation constituted less than 0.25 percent of the total.
• the iron and silicon present in the formulation constituted less than 0.07 percent each of the formulation.
• the alloy was cast and homogenized at 975°F. Thereafter, the alloy was hot rolled to a thickness of 0.2 inches. The resulting sheet was then solution treated at 975°F for about 1 hour. The sheet was then quenched in water maintained at about 70°F. Thereafter, the sheet was subjected to a stretch of 1 1/2 percent of its initial length and was then cut into specimens.
• specimens were cut to a size of 0.5 inch by 2.5 inch by 0.2 inch for precrack Charpy impact tests, a known method of measuring fracture toughness.
• Other specimens prepared for tensile strength tests were 1 inch by 4 inches by 0.2 inches.
• a plurality of specimens were then aged at 350°F for 4, 8, and 16 hours; at 325°F for 8, 16, and 48 hours; at 305°F for 8 hours; at 275°F for 16 and 40 hours; and at 250°F for 40 and 72 hours.
• Specimens aged at each of the temperatures and times were then subjected to precrack Charpy impact and tensile strength tests in accordance with standard testing procedures.
• the test values of the specimens aged at a particular temperature and time were then averaged. These average test values are set forth in the graph shown in FIGURE 1.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Extrusion Of Metal (AREA)

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Cited By (3)

Citations (7)

• 1986
  • 1986-07-03 EP EP86201174A patent/EP0250656A1/de not_active Withdrawn

Patent Citations (7)

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