Aluminum Alloys GOTChA Chart Goals High Strength Intrinsically Corrosion Resistant Aluminum Alloys for Enhanced Readiness, Improved Performance and Lower Life Cycle Costs Objectives SCC improvements-alloy with the strength of 7075-T6 and with SCC threshold equal to 75% of yield strength. No sacrifice in specific strength and toughness values. 7075-T6 mechanical properties with intrinsic corrosion resistance equivalent to that of current alloys after anodizing and without degradation of fatigue properties. 3X improvement in corrosion fatigue as compared to 7050-T7xx without degradation of other properties. Technical Challenges Approaches
Objective 1 SCC improvements-alloy with the strength of 7075-T6 and with SCC threshold equal to 75% of yield strength. No sacrifice in specific strength and toughness values. 1. Short term challenge: Fine tuning 2x9x Al alloys. (6) 2. Lack of understanding of the role of hydrogen and second phase precipitates in the stress corrosion cracking mechanism. (6) 3. Lack of quantitative modeling that accepts material s inputs. (8) 4. Lack of understanding of oxide formation and integrity on the crack growth behavior in the corrosive environment. (6) 5. Non-heat treatable Al alloy with specific mechanical strength similar to 7075-T6. (9) 6. Lack of a corrosion intensity factor and lack of ability to select accelerated corrosion or electrochemical testing to reproduce real life results. (7) 7. Variability of mechanical stress environment and corrosion environment. 8. Simultaneous improvement of all different types of corrosion resistance. (2) 9. Introduction of residual compressive stress at the surface.
Objective 1 Challenge 1 Non-heat treatable Al alloy with specific mechanical strength similar to 7075-T6. 1. Al-Mg-x x = Mn, Cr, V, Zr, Sc, Hf 2. Al-Mg-Li-x x = 3. Al-Mg-y y = Cu, Zn, Ag, etc. 4. Increase Mg and retard sensitization. 5. Optimize thermal mechanical treatment (TMT) process. 6. Amorphous/DARPA type alloys. 7. Cryomilling 8. Equal angular channeling (EACE) 9. 21 st century understanding of strengthening mechanisms.
Objective 1 Challenge 2 Lack of quantitative modeling that accepts material s inputs. 1. Empirical modeling based on mining of existing data. 2. Physics based modeling for 2xxx, 5xxx, and 7xxx alloys. 3. Identify gaps in knowledge concerning numbers 1 and 2. 4. Propose a program to close the gaps.
Objective 1 Challenge 3 Lack of a corrosion intensity factor and lack of ability to select accelerated corrosion or electrochemical testing to reproduce real life results. 1. Evaluation of existing approaches in simulating the growth of cracks in the corrosive environment. 2. Extrapolating automotive industry s approach to accelerated test method development. 3. Evaluation of simulators that include loads, cracks, and exposure to actual corrosive environments. 4. Analyze existing database and lessons learned.
Objective 2 7075-T6 mechanical properties with intrinsic corrosion resistance equivalent to that of current alloys after anodizing and without degradation of fatigue properties. 1. Lack of understanding of oxide formation and integrity. (7) 2. How to get a optimized surface layer- De-alloying, clading, gradient etc. (13) 3. Growth of surface protective oxides via high temperature oxidation. (3) 4. Surface modification: Carburization (2) 5. Self-healing surface oxides via micro-alloying or other strategies. (9) 6. Alternative anodizing. (6) 7. Incomplete understanding of how micro-structural features affect corrosion behavior. (9) 8. Development of amorphous (SAM) alloy with acceptable K IC. (5)
Objective 2 Challenge 1 How to get an optimized surface layer- De-alloying, cladding, gradient, etc. 1. Define what is the optimized surface. 2. Evaluate existing approaches to cast different compositions through thickness. 3. Evaluate methods to change the composition of the surface. Laser, spray, vapor deposition, carburization, surface diffusion treatment 4. Control oxidation by manipulating the gaseous environment.
Objective 2 Challenge 2 Self-healing surface layers via micro-alloying or other strategies. 1. Evaluate the characteristics of oxide layers based on the presence of other elements. 2. Carburizing and nitriding. 3. Explore mechanisms of self healing.
Objective 2 Challenge 3 Incomplete understanding of how micro-structural features affect corrosion behavior. 1. Evaluate and integrate existing electrochemical data regarding characteristics of micro-structural features. 2. Propose models using information and data to describe the corrosion behavior.
Objective 3 3X improvement in corrosion fatigue as compared to 7050-T7xx without degradation of other properties. 1. Short term challenge: Fine tuning 2x9x Al alloys. (11) 2. Lack of understanding of oxide formation and integrity on the crack growth behavior in the corrosive environment. (10) combine 2 & 4 3. Higher intrinsic da/dn resistance. (2) 4. Lack of understanding of micro-structural features that gives rise to crack initiation sites. (13) 5. Lack of understanding of damage induced by corrosion and its transition to crack growth. (11) 6. Lack of understanding of how to control the critical pit size. (1) 7. Developing an affordable and producible alloy with high pitting resistance. (3)
Objective 3 Challenge 1 Lack of understanding of micro-structural features that gives rise to crack initiation sites. 1. Identify the crack initiation sites of 2xxx, 5xxx, and 7xxx in various tempers. 2. Identify the effect of micro-structural features such as grain boundary or second phase particles or deformation on pitting formation. 3. Propose mechanisms associated with the formation of crack initiation sites.
Objective 3 Challenge 2 Lack of understanding of damage induced by corrosion and its transition to crack growth. 1. Characterize pit morphology and size in 2xxx, 5xxx, and 7xxx alloys in various tempers. 2. Establish a correlation between their propensity to crack initiation.
Objective 3 Challenge 3 Short term challenge: Fine tuning 2x9x Al alloys. 1. Establish the effect of alloy chemistries on corrosion fatigue performance and understand the mechanisms by evaluating the fatigue performance in corrosive environment for the highly corrosion resistant Al-Cu-Li alloys, 2098,2050,2198,2099,2199 and 2195. 2. Define testing methodology of the fatigue performance in corrosive environments. 3. Propose fine tuning of product.
Objective 1 Objective 2 Objective 3 SCC improvements-the threshold strength of 7075-T6 is 75% of the yield strength. No sacrifice in specific strength and toughness values. 1. Short term challenge: Fine tuning 2x9x Al alloys. (6) 2. Lack of understanding of the role of hydrogen and second phase precipitates in the stress corrosion cracking mechanism. (6) 3. Lack of quantitative modeling that accepts material s inputs. (8) 4. Lack of understanding of oxide formation and integrity on the crack growth behavior in the corrosive environment. (6) 5. Non-heat treatable Al alloy with specific mechanical strength similar to 7075-T6. (9) 6. Lack of a corrosion intensity factor and lack of ability to select accelerated corrosion or electrochemical testing to reproduce real life results. (7) 7. Variability of mechanical stress environment and corrosion environment. 8. Simultaneous improvement of all different types of corrosion resistance. (2) 9. Introduction of residual compressive stress at the surface. 7075-T6 mechanical properties, corrosion resistance equivalent to anodizing and no fatigue debit. 1. Lack of understanding of oxide formation and integrity. (7) 2. How to get a optimized surface layer- Dealloying, clading, gradient etc. (13) 3. Growth of surface protective oxides via high temperature oxidation. (3) 4. Surface modification: Carburization (2) 5. Self-healing surface oxides via microalloying or other strategies. (9) 6. Alternative anodizing. (6) 7. Incomplete understanding of how microstructural features affect corrosion behavior. (9) 8. Development of amorphous (SAM) alloy with acceptable K IC. (5) 3X improvement in corrosion fatigue as compared to 7050-T71. 1. Short term challenge: Fine tuning 2x9x Al alloys. (11) 2. Lack of understanding of oxide formation and integrity on the crack growth behavior in the corrosive environment. (10) combine 2 & 4 3. Higher intrinsic da/dn resistance. (2) 4. Lack of understanding of micro-structural features that gives rise to crack initiation sites. (13) 5. Lack of understanding of damage induced by corrosion and its transition to crack growth. (11) 6. Lack of understanding of how to control the critical pit size. (1) 7. Developing an affordable and producible alloy with high pitting resistance. (3)