Microstructure and homogenization process of semi-continuous casting 7136 ultra high-strength aluminum alloy
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摘要: 以半連續鑄造7136鋁合金為研究對象, 以鑄態組織分析為基礎, 采用雙級均勻化. 結果表明: 與其他7×××系鋁合金相比, 7136鋁合金鑄態組織沒有明顯的層片狀α(Al)+T共晶相的特征, 也沒有發現S相的存在. 基體中的彌散相為微米級的圓形或棒狀MgZn2相, Mg元素和Zn元素隨著液態合金的凝固, 在Al基體中以MgZn2相的形式析出, 為了平衡Mg元素和Zn元素的分配系數, Mg元素和Zn元素從液態向固態遷移, 這也是使得晶內Zn元素和Mg元素偏高的原因. 經過462℃, 24 h單級均勻化, 殘留相大致消除. 隨著均勻化時間的延長, 殘留相有減少的趨勢, 但作用相對較小. 經過450℃, 24 h+470℃, 24 h雙級均勻化, 差示掃描量熱法獲取的峰值非常小, 晶間除了少量高熔點Al7Cu2Fe相殘留, Al2Cu等其他相已基本消除, 均勻化效果顯著.
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關鍵詞:
- 7136超高強鋁合金 /
- 半連續鑄造 /
- MgZn2相 /
- 鑄態組織 /
- 均勻化熱處理
Abstract: The 7×××series aluminum alloy is mainly produced using semi-continuous water-cooled casting with this method, the solidification speed of the alloy is fast, leading to different degrees of dendrite segregation and non-equilibrium eutectic structure in the ingot. This also results in non-uniformity of composition and structure. Further, it adversely affects the subsequent cutting process and comprehensive performance of the alloy. Therefore, ingot homogenization becomes an indispensable and very critical process for the elimination of segregation. There is much research on Al-Zn-Mg-Cu alloys at home and abroad at the present. This research mainly concentrates on alloys such as 7075, 7050, 7150 and 7055. The content of the main alloying elements of these alloys is mostly around 10%. However, at present, there is not much research on alloy materials with a strength and main alloying element content exceeding 12.5%. The main alloy element content of 7136 aluminum alloy is about 13.5%. In 7136 aluminum alloy, the main alloy element content is high and the cast microstructure characteristics and homogenization treatment conditions are very different from other 7×××series aluminum alloys. In this paper, semi-continuous casting 7136 aluminum alloy was taken as the research object, based on the as-cast microstructure analysis, using two-stage homogenization. The results show that, compared with the other 7×××series aluminum alloys, the cast microstructure of 7136 aluminum alloy has no obvious lamellar Al(Al)+T eutectic phase characteristics, and no S phase exists. The dispersed phase in the matrix is a micron-sized round or rod-shaped MgZn2 phase. The Mg and Zn were precipitated as MgZn2 phase in the Al matrix as the liquid alloy solidified. In order to balance the partition coefficients of the Mg and Zn, the two metals converted from the liquid to the solid state, which explained why the Zn and Mg crystal contents were high. After a single stage of homogenization at 462℃, 24 h, the residual phase was substantially eliminated. As the homogenization time increased, the residual phase tended to decrease, but the effect was relatively small by this method. After the 7136 aluminum alloy was homogenized for two stages at 450℃, 24 h and 470℃, 24 h. The peak values obtained by differential scanning calorimetry were very small, except for a small amount of high-melting Al7Cu2Fe phase remaining between the crystals. Al2Cu and other phases were basically eliminated and the homogenization effect was significant. -
圖 1 7136鋁合金鑄態組織的光學顯微分析. (a)邊緣；(b)1/2半徑；(c)中心
Figure 1. Optical microscopic analysis of the cast microstructure of the 7136 aluminum alloy: (a)edge; (b)1/2 radius; (c)center
圖 2 7136鋁合金鑄態組織掃描電鏡分析.(a)中心樣品; (b)邊部樣品
Figure 2. SEM analysis of the cast microstructure of the 7136 aluminum alloy: (a)center of the sample; (b)edge of the sample
圖 3 7136鋁合金鑄態組織線掃描分析.(a)鑄態組織; (b)線掃描
Figure 3. Line scanning analysis of the cast microstructure of the 7136 aluminum alloy: (a) cast microstructure; (b)line scan
圖 4 7136鋁合金鑄態組織面掃描分析. (a)Cu元素；(b)Mg元素；(c)Zn元素
Figure 4. Surface scanning analysis of the cast microstructure of the 7136 aluminum alloy: (a)Cu; (b)Mg; (c)Zn
圖 5 7136鋁合金鑄態組織差示掃描量熱法曲線
Figure 5. DSC curve of the cast microstructure of the 7136 aluminum alloy
圖 6 不同保溫溫度條件下的均勻化組織. (a)455 ℃，24 h；(b)457 ℃，24 h；(c)459 ℃，24 h；(d)461 ℃，24 h；(e)463 ℃，24 h；(f)465 ℃，24 h；(g)467 ℃，24 h；(h) 469 ℃，24 h
Figure 6. Homogenized microstructure at different holding temperatures: (a)455 ℃, 24 h; (b)457 ℃, 24 h; (c)459 ℃, 24 h; (d)461 ℃, 24 h; (e)463 ℃, 24 h; (f)465 ℃, 24 h; (g)467 ℃, 24 h; (h) 469 ℃, 24 h
圖 7 鑄態和單級均勻化后的差示掃描量熱法曲線
Figure 7. DSC curves after as-cast and single-stage homogenization
圖 8 7136鋁合金在462 ℃條件下保溫不同時間的光學顯微組織. (a) 462 ℃，36 h；(b)462 ℃，48 h；(c)462 ℃，72 h
Figure 8. Optical microstructure of the 7136 aluminum alloy kept at 462 ℃ for different times: (a) 462 ℃, 36 h; (b)462 ℃, 48 h; (c)462 ℃, 72 h
圖 9 7136鋁合金在462 ℃條件下保溫不同時間的掃描電鏡圖. (a) 462 ℃，36 h；(b)462 ℃，48 h；(c)462 ℃，72 h
Figure 9. SEM image of the 7136 aluminum alloy kept at 462 ℃ for different times: (a) 462 ℃, 36 h; (b)462 ℃, 48 h; (c)462 ℃, 72 h
圖 10 7136鋁合金雙級均勻化的掃描電鏡圖(低倍). (a) 450 ℃，24 h+470 ℃，12 h; (b) 450 ℃，24 h+470 ℃，24 h
Figure 10. SEM image of two-stage homogenization of the 7136 aluminum alloy (low magnification): (a)450 ℃, 24 h+470 ℃, 12 h; (b) 450 ℃, 24 h+470 ℃, 24 h
圖 11 7136鋁合金雙級均勻化的掃描電鏡圖(高倍). (a) 450 ℃, 24 h+470 ℃, 12 h; (b) 450 ℃, 24 h+470 ℃, 24 h
Figure 11. SEM image of two-stage homogenization of the 7136 aluminum alloy(high magnification): (a) 450 ℃, 24 h+470 ℃, 12 h; (b) 450 ℃, 24 h+470 ℃, 24 h
圖 12 鑄態、單級均勻化和雙級均勻化后的差示掃描量熱法曲線
Figure 12. DSC curves after as-cast, single-stage homogenization and two-stage homogenization
表 1 7136鋁合金成分(質量分數)
Table 1. Composition of 7136 aluminum alloy?
% 牌號 Zn Mg Cu Zr Cr Mn Ti Fe Si 7136 8.4~9.4 1.8~2.5 1.9~2.5 0.1~0.2 0.05 0.05 0.1 0.15 0.12 實測成分 9.31 2.13 2.11 0.12 < 0.01 < 0.01 0.018 0.077 0.012 
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位置 Al Mg Zn Cu Fe 1 74.48 0.92 3.09 21.50 0.01 2 71.68 0.91 3.25 24.09 0.01 3 87.39 0 1.61 11.00 0 4 93.44 2.19 4.38 0 0
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位置 Al Mg Zn Cu 1 75.79 0 0 24.21 2 71.06 1.72 1.09 26.13 3 61.90 0 0 38.10 4 78.66 0 0 21.34 5 48.82 9.3 0 41.88
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位置 Al Mg Zn Cu Fe 1 54.88 1.18 4.22 35.46 4.26 2 62.54 1.33 6.86 27.31 1.96 3 59.26 1.78 2.84 32.32 3.80 4 62.13 1.48 3.46 27.12 5.81
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