2091 Aluminum Alloy Plate

2091 aluminum-lithium alloy, American wrought aluminum and aluminum alloy. 2091 is a medium-strength aluminum alloy, 8% lower in density than 2024-T3, and 7% higher in elastic modulus. The 2219 aluminum alloy series is developed to improve the high-temperature properties of the 2000 series, with low thermal cracking tendency and good weldability. 2091 aluminum alloy is slightly higher in hot ductility than 2219 aluminum alloy, and has a higher sensitivity to hot cracking, which is the disadvantage of 2091 aluminum alloy. 

In the cooling process, the ductility of 2091 recovers slowly, and the ductility cannot be fully recovered after being heated to the zero-strength temperature. There is little difference between the axial and lateral hot ductility of 2091 aluminum alloy. The zero ductility temperature is 540℃, at which the temperature changes from transgranular to epitaxial fracture. 

The reason for the loss of ductility of 2091 aluminum alloy is because the T2 phase accumulates at the grain boundary, resulting in unbalanced eutectic melting, which leads to the liquefaction of the grain boundary. During the cooling process, the T2 phase cannot be completely recovered and cavities are left. Using NST as the peak temperature of the thermal cycle is better to measure the high temperature thermal cracking sensitivity of 2091-T3.

2091 aluminum alloy was developed to be a damage-tolerant alloy with 8% lower density and 1% higher modulus than 2024-T3, a major high-toughness damage-tolerant alloy currently used for most aircraft structures. 2091 aluminum alloy is also suitable for use in secondary structures where high strength is not critical.

2091 aluminum alloy has been registered with the Aluminum Association. A variety of tempers are being developed to offer useful combinations of strength, corrosion resistance, damage tolerance, and fabricability. The microstructure of 2091 varies according to product thickness and producer; in general, gages above 3.5 mm have an unrecrystallized microstructure, and lighter gages feature an elongated recrystallized grain structure.

In general, the behavior of 2091 aluminum alloy is similar to that of other 2xxx and 7xxx alloys. Material characteristics that have been cause for concern in other aluminum-lithium alloys are of less concern in 2091. Alloy 2091 depends less on cold work to attain its properties than does 2024. The properties of 2091 after elevated-temperature (up to 125oC) exposure are relatively stable in that changes in properties during the lifetime of a component are acceptable for most commercial applications.

The exfoliation resistance of 2091-T84, like that of 2024, varies depending on the microstructure of the product and its quench rate. The more unrecrystallized the structure, the more even the exfoliation attack. However, the exfoliation resistance of 2091 is generally comparable to that of similar gages of 2024-T3.

The microstructural relationship for stress-corrosion cracking in sheet products is the converse of that for exfoliation. As the microstructure becomes more fibrous, the SCC threshold increases. For thicker unrecrystallized structures and thinner elongated recrystallized structures, it is possible to attain an SCC threshold of 240 MPa, which is quite good compared to that of 2024-T3. For thinner products, the threshold varies by gage and producer; it may be as low as 50 to 60% of the yield strength or as high as 75% of the yield strength.

Although fatigue testing on 2091 has been done by a number of labs, producers, and users, the results have been difficult to interpret. The results for 2091 have been superior to those for 2024, roughly equivalent to those for 2024, or inferior to those for 2024. In general, the consensus is that under controlled and similar circumstances, the fatigue properties of 2091-T84 are sufficient to allow it to be used as a substitute for 2024.

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Related 2000 Series Aluminum Alloy Materials