| Stage | Typical property | Key technique | Typical alloy | | 1st generation | Static strength | Peak ageing, | 7A04(LC4), 2A12(LY12), | | 1950s~1970s | | Cr, Mn-additions | 2014(D10) | | 2nd generation | Stress-corrosion cracking | Over ageing | 7A09-T73, T74(7075-T73, T74) | | 1970s~1980s | resistant, damage tolerant | | (LC9), 2219(LY16) | | 3rd generation | High strength, | Purifying, Zr-addition | 7475, 2124, 2324, 7050 | | 1980s~2000s | high toughness, | Fine constituent particles, | 7B04, 2D70, 2D12, 2B06 and | | corrosion-resistant | two-step ageing, lowering | 5A90, 1420(Al-Li) | | | density | | | 4th generation 2000s~ | High strength, high toughness, | Further purifying, multi-stage | 7A55, 2A97, 2E12, 7B50 | | corrosion-resistant, high | heat treatment, Li alloying | | | damage-tolerant | | | | 5th generation 2005s~ | Low quench-sensitivity, | Lowering solvus, addition of | 7A50, 7A85, 7B85 | | high comprehensive properties | slower diffusing species | |
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