Effects of Heat Treatment on the Microstructure and Sensitization Properties of Al-Mg Alloy

• Main Authors: Ren Yu Chen, 陳仁郁
• Other Authors: Cheng Chyuan Lai
• Format: Others
• Language: zh-TW
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/10769961157702231267

博士 === 國防大學理工學院 === 國防科學研究所 === 102 === This study elucidates how annealing temperature affects the mechanical properties and sensitization of 5083-H116 aluminum alloys. The properties of annealed and sensitized samples of 5083-H116 were investigated by microhardness measurements, tensile testing, scanning electron microscope (SEM) and optical microscopy (OM). Nitric acid mass loss testing (ASTM G67 NAMLT) and slow strain rate testing (SSRT) were conducted to examine the influence of different microstructure on the intergranular corrosion (IGC) and stress corrosion cracking (SCC) susceptibility of 5083-H116. Electrical conductivity was employed as indirect evidence to assess the microstructural evolution in 5083-H116 Al-Mg alloys after annealing at various temperatures and sensitization treatment. In addition, this study focuses on the effects of a planed heating treatment to the sensitization reversing of a sensitized specimen. The results indicated that the annealing process will consequently impact their mechanical and anti-corrosion properties of the structures. The mechanical properties of the alloys became rapidly worse upon annealing between 250°C and 350°C. The distribution and shapes of β-phase particles markedly affected the sensitization. The alloys annealed below 200 °C and upon 300 °C, high IGC and SCC susceptibility were experienced, induced β-phase (Al3Mg2) precipitation in the form of a continuous layer along the grain boundaries. High IGC and SCC resistance attained after annealed at the temperature range 200~250 °C due to the discontinuous β-phase precipitated at grain boundaries. Additionally, the electrical conductivity is more sensitive to Mg solute atoms in solid solution than to dislocation density. The β phase precipitated during sensitization increased electrical conductivity, especially in recovered structure. The degree of sensitization (DoS) was closely related to the microstructure and increased with decreasing electrical conductivity under sensitization. Exposing at the temperatures of 240°C for 10~30 minutes could effectively improve the sensitization of the 5083-H116 alloys.