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1 Vol.21 No.5 The Chinese Journal of Nonferrous Metals May (2011) A14 1, 1, 2, 1, ( ) 2A14 (CCT ) DSC SEM 2A14 2A14 CCT (TEM) 2A ~ /s 20 mm 2A CCT 2A14 (CCT ) TG 151 A Continuous cooling transformation curve for 2A14 aluminum alloy and its application LI Hong-ying 1, ZHAO Yan-kuo 1, TANG Yi 2, WANG Xiao-feng 1, DENG Yun-zhe 1 (1. School of Materials Science and Engineering, Central South University, Changsha , China; 2. Institute of Pumping, SANY Heavy Industry Co., Ltd., Changsha , China) Abstract: The continuous cooling transformation (CCT) curve of 2A14 aluminum alloy and its application were studied. The solutionizing temperature was ascertained by DSC analysis and SEM observation. Electrical resistance temperature curves of 2A14 alloy in the continuous cooling processes after solid solution treatment were obtained by in-situ resistance measurement. Messages of the phase transformation were judged by analyzing the slope change of the obtained curves. The CCT diagram for Al-Cu-Mg alloy was plotted. The microstructure evolution during the cooling was examined by TEM observation. The results show that the appropriate solid solution temperature is 505. The phase transformation starting temperature decreases with the increase of cooling rates when the cooling rate is slow, but when the cooling rate is a little higher the phase transformation starting temperature increases suddenly. The phase transformation mainly takes place between 140 and 380. The critical cooling rate for preventing the phase transformation is above 38.5 /s. It is better for 2A14 plates with the thickness of 20 mm to quench by 60 or 100 water. Interrupted quenching process can be established according to the tested CCT diagram to decrease quenching stress utmost and inhibit the precipitation of the secondary phases at the same time. Key words: 2A14 alloy; continuous cooling transformation (CCT) curve; in-situ electrical resistance; phase transformation; cooling rate : lhying@mail.csu.edu.cn

2 21 5 2A [1] (TTT TTP CCT ) CCT [2] CCT [3 5] [6 8] 2A A04 CCT [9 11] Al-Cu-Mg [12] Al-Cu-Mg CCT 2A14 CCT CCT 1 20 mm 2A14 1 [11] 1 2A14 Table 1 Chemical composition of 2A14 alloy (Mass fraction, %) Zn Mg Cu Mn Ti Fe Si Al Bal. TecnaiG 2 20 CCT 30% 20 mm 57 mm 85 mm CCT CCT K/min DSC ( ) 516 ( ) 1 h SEM 2(a) 2(b) (a) h [13] h DSC QUANTA 200 ( ) 1 2A14 DSC Fig.1 DSC curves of forged 2A14 alloy

3 [14] A14 SEM Fig.2 SEM images of 2A14 alloy at different solution temperatures: (a) 505, 1 h; (b) 516, 1 h 3 50~ (a) (Matthiessen rule) [14] 4.29 /s 3(b) 3 2A14 Fig.3 Representative electrical resistance temperature curves of 2A14 alloy at different quenching rates: (a) /s; (b) 4.29 /s; (c) 38.5 /s

4 21 5 2A A14 Table 2 Phase transformation temperatures of 2A14 alloy at different cooling rates Sample No. Cooling rate/ ( s 1 ) Starting temperature/ Finishing temperature/ a b c d e f g h (c) 5 5(a) 2 5(b) (505 ) 1 (430 ) 1 (250 ) 1 (50 ) 3(c) 350~470 2A /s CCT β 5 Fig.5 Schematic diagram for verification experiment by quenching: (a) Comparison of cooling curves; (b) Schematic diagram of quenching temperature 4 2A14 CCT Fig.4 CCT diagram for 2A14 aluminum alloy 6 (323 ) 6(a) (b) 6(c) (d) 50 6(e) (f)

5 TEM Fig.6 TEM images of samples quenched from different temperatures: (a) 505 ; (b) 430 ; (c), (d) 250 ; (e), (f) 50 6(c) ( ) 7 Al Cu Al 2 Cu 2 Al 2 Cu 2.3 CCT 4 7 CCT [10 11] ( 4 e)

6 21 5 2A A14 EDS Fig.7 EDS result of coarse precipitated phases in 2A14 alloy GP GP 4 e θ g θ GP CCT 4 140~ /s 20 mm CCT /s 8 2A CCT CCT CCT 8 CCT Fig.8 Schematic diagram of positions of central cooling curves of thick sample in CCT diagram

7 CCT s 40~45 s 3 1) 2A14 2A14 CCT 2) h 2A14 140~ /s 3) 20 mm 2A CCT REFERENCES [1] LIU S D, ZHONG Q M, ZHANG Y, LIU W J, ZHANG X M, DENG Y L. Investigation of quench sensitivity of high strength Al-Zn-Mg-Cu alloys by time temperature properties diagrams[j]. Materials and Design, 2010, 31: [2] STALEY J T. Quench factor analysis of aluminum alloy[j]. Materials Science and Technology, 1987, 3: [3] HERDING T, KESSLER O, HOFFMANN F, MARY P. An approach for continuous cooling transformation (CCT) diagrams of aluminum alloys[j]. Materials Science Forum, 2002, 396/402: [4] KESSLER O, BARGEN R, HOFFMANN F, ZOCH H W. Continuous cooling transformation (CCT) diagram of aluminum alloy Al-4.5Zn-1Mg[J]. Materials Science Forum, 2006, 519/521: [5] MILKEREITA B, KESSLER O, SCHICK C. Recording of continuous cooling precipitation diagrams of aluminium alloys[j]. Thermochimica Acta, 2009, 492(1/2): [6] FURLANI A M, STIPCICH M, ROMERO R. Phase decomposition in a β Cu-Zn-Al-Ti-B shape memory alloy[j]. Materials Science and Engineering A, 2005, 392(1/2): [7] TEIXEIRA J, APPOLAIRE B, AEBY-GAUTIER E, DENIS S, CAILLETAUD G, SPAAETH N. Transformation kinetics and microstructures of Ti17 titanium alloy during continuous cooling[j]. Materials Science and Engineering A, 2007, 448(1/2): [8] MATSUMOTO H. Electrical resistivity of NiTi with high transformation temperature[j]. Journal of Alloys and Compounds, 2004, 370(1/2): [9] LI H Y, GENG J F, ZHENG Z Q, WANG C J, SU Y, HU B. Continuous cooling transformation curve of a novel Al-Cu-Li alloy[j]. Transactions of Nonferrous Metals Society of China, 2006, 16(5): [10],,,,. Al-Zn-Mg-Cu [J]., 2008, 18(9): LI Hong-ying, TANG Yi, ZENG Zai-de, WANG Fa-yun, SUN Yuan. Testing of continuous cooling transformation of curve Al-Zn-Mg-Cu alloy[j]. The Chinese Journal of Nonferrous Metals, 2008, 18(9): [11],,,,,,. 7A04 [J]., 2010, 20(4): LI Hong-ying, WANG Xiao-feng, TANG Yi, DENG Yun-zhe, HUANG Yu, SUN Yuan, WANG Fa-yun. Testing and study of continuous cooling transformation curves of 7A04 aluminum alloy[j]. The Chinese Journal of Nonferrous Metals, 2010, 20(4): [12] KOVARIK L, COURT S A, FRASER H L, MILLS M J. GPB zones and composite GPB/GPBII zones in Al-Cu-Mg alloys [J]. Acta Materialia, 2008, 56(17): [13]. 2A14-T6 [J]., 2004(9): WANG Li. Study of age treatment system of 2A14-T6 large sized aluminum alloy bars[j]. Light Metals, 2004(9): [14]. [M]. :, 2009: LONG Yi. Physical properties of materials[m]. Changsha: Central South University Press, 2009: ( )