T6和T78时效工艺对Al-Mg-Si-Cu合金显微结构和性能的影响  

EFFECTS OF T6 AND T78 TEMPERS ON THE MICROSTRUCTURES AND PROPERTIES OF Al-Mg-Si-Cu ALLOYS

作　　者：李祥亮[1] 陈江华[1] 刘春辉[1] 冯佳妮[1] 王时豪[1] 

机构地区：[1]湖南大学材料科学与工程学院,长沙410082

出　　处：《金属学报》2013年第2期243-250,共8页Acta Metallurgica Sinica

基　　金：国家重点基础研究发展计划项目2009CB623704;国家自然科学基金项目51171063;湖南省高校科技创新团队项目;湖南省研究生科研创新项目;Gatan中国博士生奖学金项目资助~~

摘　　要：借助显微硬度测试、电导率测试、浸泡腐蚀实验、SEM，TEM和元素面扫描，研究了T6和T78时效工艺对A1-0．75Mg-0．75Si-0．8Cu（质量分数，％）合金显微结构和性能的影响．结果表明，实验合金在T6峰值时效（180℃，8h）时，硬度为128．3HV，电导率为27．3x10。S／m．在T6（180℃，5h）基础上，分别进行温度为195，205和215℃的二级时效，即T78时效工艺，随二级时效时间的延长，合金硬度总体变化趋势为先降低后升高，而电导率值逐渐增大；最佳T78工艺为f180℃，5h）＋（195℃，2h），此时合金的硬度最高，为129．2HV，电导率为27．6x10^6S／m．TEM观察发现，T6峰值时效时，晶粒内主要析出针状的卢”相，经T78双级时效处理后，晶粒内析出大量的板条状析出相，而晶界无析出带仅稍有变化．T78工艺能在保持力学性能的同时，大幅提高耐晶间腐蚀性能，其原因是晶粒内形成了表面有Cu富集的板条状析出相．晶粒内析出大量板条状强化相，使得合金硬度与T6峰值相当，同时Cu偏聚在析出相与Al基体界面处，促使更多Al基体中的Cu析出，基体与无析出带（PFZ）电位差大大降低，使得其抗晶间腐蚀性能大大提高．Although A1MgSi （6000-series） are generally considered to have better corrosion resistance than other aluminum alloys, it may introduce susceptibility to intergranular corrosion （IGC） by some factors, for instance, improper thermo-mechanical treatment and high Cu content. So the T78 treatment has been designed to desensitize it to IGC. In this paper, effects of T6 and T78 tempers on the microstructures and properties of an A1-0.75Mg-0.75Si-0.8Cu （mass fraction, %） were investigated by hardness test, electric conductivity test, accelerated corrosion test, SEM, TEM and energy dispersive X-ray elemental mapping. The hardness and conductivity of the T6 peakaged sample, which was obtained by artificial aging for 8 h at 180 I2, were 128.3 HV and 27.3 x 10^6 S/m,respectively. T78 tempers involved a first step aging （180 ℃, 5 h） followed by a second step aging at 195, 205 and 215 ℃, respectively. With the prolonging of second step aging, the hardness firstly decreased then increased, while the conductivity increased gradually. The optimum T78 process was （180 ℃, 5 h）＋（195 ℃, 2 h）, at which condition the hardness was 129.2 HV and the electric conductivity was 27.6X10^6 S/m. TEM observation results show that it was mostly needle-like 13＂ phase in the A1 matrix for the peak-aged sample. After T78 treatment, a large amount of lath-like precipitates formed in the matrix, while the precipitate free zones （PFZ） broadened slightly. The segregation of Cu was found at the interface between lath-like precipitates and the matrix, so more Cu precipitated out from the A1 matrix and thus reduced the electrochemical potential difference between the PFZ and the matrix. The above finding may explain why T78 temper can desensitize intergranular corrosion without sacrificing strength.

关 键 词：铝合金 析出相 晶界 晶间腐蚀 显微结构 

分 类 号：TG113[金属学及工艺—物理冶金] TG178[金属学及工艺—金属学]