Case Study Effects of annealing temperature on the mechanical properties and sensitization of 5083-H116 aluminum alloy Ren-Yu Chen 1 , Hsiao-Yeh Chu 2 , Cheng-Chyuan Lai 3 and Chih-Ting Wu 4 Abstract This study elucidates how annealing temperature affects the mechanical properties and sensitization of 5083-H116 aluminum alloys. Nitric Acid Mass Loss Test was conducted to investigate the sensitization behavior of the annealed specimens. The results indicated that the mechanical properties were more sensitive to the annealing temperature than to the annealing time. The mechanical properties of the alloys became rapidly worse upon annealing between 250 and 350  C. 5083-H116 aluminum alloy became sensitized and susceptible to intergranular corrosion at an annealing tem- perature of 175  C for 48 h. The distribution and shapes of b-phase particles markedly affected the sensitization. Exposing at the temperatures of 230–250  C for 10–30 min could effectively improve the sensitization of the 5083-H116 alloys. Keywords 5083-H116, sensitization, b-phase, intergranular corrosion, Nitric Acid Mass Loss Test Date received: 2 February 2013; accepted: 4 October 2013 Introduction 5xxx Al-Mg alloys, such as 5083, are medium- strength, non-heat treatable wrought aluminum alloys. They have been widely used in marine struc- tures owing to their light weight, weldability, and favorable corrosion resistance. These Al-Mg alloys, which exhibit a range of useful material properties, are highly desired for being used in fast sea transpor- tation for commercial and military applications. Since the 1950s, U.S. Navy has preferred to use magnesium- strengthened 5xxx alloys, which are also favored for use in new high performance vessels. 1,2 It is well known that the strength of Al-Mg alloys increases with increasing Mg content, but raising temperature during the annealing process lowers the strength of Al-Mg alloys. 3 In addition, although increasing Mg content can enhance strength, it may be accompanied by a decrease in corrosion resistance. 4 5xxx Al-Mg alloys that contain more than 3 wt.% Mg are supersaturated at room temperature. The excess Mg solute atoms tend to precipitate out as b-phase (Mg 2 Al 3 ) particles, distributed along the grain boundaries during prolonged aging at room temperature, or after shorter periods of exposure at slightly elevated temperatures (65–200  C). 5–7 As displayed in Figure 1, 8 marine alloys such as 5086 (3.5–4.5 Mg), 5083 (4.0–4.9 Mg), and 5456 (4.7–5.5 Mg) become sensitized, and thus susceptible to corrosion, upon exposure to temperatures in the range that is indicated by the hashed area (in the a þ b phase field). Since the b-phase is electrochem- ically more active than the Al-matrix, plates destabil- ize over time and are susceptible to exfoliation, intergranular corrosion (IGC), and stress corrosion cracking (SCC) in stress and corrosive environ- ments. 4,9 Such phenomena are normally referred to as ‘‘sensitization,’’ 10 especially in the heat-affected zone (HAZ) of a weld or in deck and superstructure 1 School of Defense Science, Chung Cheng Institute of Technology, National Defense University, Taoyuan, Taiwan 2 Department of Mechanical Engineering, Kun Shan University, Tainan, Taiwan 3 Department of Mechatronic, Energy and Aerospace Engineering, Chung Cheng Institute of Technology, National Defense University, Taoyuan, Taiwan 4 Army Academy R.O.C., Taoyuan, Taiwan Corresponding author: Hsiao-Yeh Chu, Department of Mechanical Engineering, Kun Shan University, Tainan 71003, Taiwan. Email: hsiaoyeh@mail.ksu.edu.tw Proc IMechE Part L: J Materials: Design and Applications 0(0) 1–8 ! IMechE 2013 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/1464420713512249 pil.sagepub.com at PENNSYLVANIA STATE UNIV on September 16, 2016 pil.sagepub.com Downloaded from