1、_SAE Technical Standards Board Rules provide that: “This report is published by SAE to advance the state of technical and engineering sciences. The use of this report is entirely voluntary, and its applicability and suitability for any particular use, including any patent infringement arising theref
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5、firmed 2013-05 Superseding ARP823D Minimizing Stress-Corrosion Cracking in Wrought Heat-Treatable Aluminum Alloy Products RATIONALEARP823E has been reaffirmed to comply with the SAE five-year review policy. 1. SCOPE 1.1 The purpose of this recommended practice is to provide the aerospace industry wi
6、th recommendations concerning minimizing stress-corrosion cracking (SCC) in wrought high-strength aluminum alloy products. 1.2 The detailed recommendations are based on practical engineering experience and reflect those design practices and fabricating procedures which have been found to be most eff
7、ective in minimizing stress-corrosion cracking in wrought high-strength aluminum alloy products. 1.3 This ARP provides general guidelines. For further information see references in 4.3. 2. REFERENCES 2.1 Applicable Documents The following publications form a part of this document to the extent speci
8、fied herein. The latest issue of SAE publications shall apply. The applicable issue of other publications shall be the issue in effect on the date of the purchase order. In the event of conflict between the text of this document and references cited herein, the text of this document takes precedence
9、. Nothing in this document, however, supersedes applicable laws and regulations unless a specific exemption has been obtained. 2.1.1 ASTM Publications Available from ASTM International, 100 Barr Harbor Drive, P.O. Box C700, West Conshohocken, PA 19428-2959, Tel: 610-832-9585, www.astm.org.ASTM G 64
10、Classification of Resistance to Stress-Corrosion Cracking of High-Strength Aluminum Alloys (Volume 03.02 of the ASTM 1986 Book of Standards) SAE ARP823E Page 2 of 4 2.1.2 NASA Publications Available from NASA, Documentation, Marshall Space Flight Center, AL 35812, www.nas.nasa.gov.MSFC-SPEC-522A Des
11、ign Criteria for Controlling Stress Corrosion Cracking, issued 1977 November 18 by George C. Marshall Space Flight Center MSFC-STD-3029 Guidelines for the Selection of Metallic Materials for Stress-Corrosion Cracking Resistance in Sodium Chloride Environments Materials, Processes, and Manufacturing
12、Department Metallic Materials and Processing Group 2.1.3 U.S. Government Publications Available from the Document Automation and Production Service (DAPS), Building 4/D, 700 Robbins Avenue, Philadelphia, PA 19111-5094, Tel: 215-697-6257, http:/assist.daps.dla.mil/quicksearch.MIL-HDBK-1568 Materials
13、and Processes for Corrosion Prevention and Control in Aerospace Weapons Systems 2.1.4 Other Publications Metallic Materials Properties Development and Standardization (MMPDS-03)NBS Monograph 156, “Stress Corrosion Cracking Control Measures”, by B. F. Brown, Chapter 4 on Aluminum Alloys, 1977 June 3.
14、 GENERAL Stress-corrosion cracking failures of wrought, high-strength aluminum alloy parts have been attributed to the following combination of factors: a. Presence of a sustained surface tensile stress developed as a result of assembly stresses and/or residual stresses due to heat treatment, formin
15、g, or service stresses acting in a direction perpendicular to the plane of predominant grain flow. b. Presence of a corrosive environment, which need not be severe (atmospheric water vapor may be sufficient), and c. Existence, in the product, of a metallurgical condition which makes the product susc
16、eptible to stress-corrosion cracking. 3.1 Al-Cu-Mg alloys and Al-Li alloys of the 2XXX series, 5XXX alloys with magnesium greater than 3%, Al-Zn-Mg and Al-Zn-Mg-Cu alloys of the 7XXX series are most susceptible to stress-corrosion cracking especially in the short-transverse direction. Tempers of par
17、ticular concern are T3XX and T6X in 2XXX and 7XXX alloys respectively. MMPDS-3 which superseded MIL-HDBK 5 provides specific threshold stress levels and exposure times. Acceptance criteria and corrosion capability for 5XXX alloys with magnesium greater than 3%, specified for marine use and citing H1
18、16 and H321, are defined by ASTM B 928. 3.1.1 Control of the fabrication process is important for the avoidance of stress-corrosion cracking susceptibility in select 2XXX and 7XXX alloys in the T8 and T7 tempers respectively. This specifically applies to peak aged T8XX and over-aged tempers such as
19、T73XX, T74XX, T76XX and T79XX. These products were engineered to guarantee a demonstrated level of Stress Corrosion and Exfoliation Resistance. Tensile loading in the short transverse direction is an important design parameter. Achieving this level of corrosion resistance requires very good understa
20、nding of the aging process and controls which assure consistent response. Quality assurance tests include conductivity and tensile properties. SAE ARP823E Page 3 of 4 4. RECOMMENDATIONS 4.1 General Applied stresses in the short-transverse direction should be minimized. Besides material susceptibilit
21、y, residual forming stresses, stresses from machining, and stresses from assembly or misfit of parts can contribute to stress-corrosion cracking. Such stresses should not be overlooked in the design phase. Use alloys and tempers resistant to SCC. Use stress-relieved parts. Perform severe forming on
22、product in the annealed condition, followed by heat treatment, if required. Perform forming and straightening on newly quenched product to lessen forming stresses. Avoid fitup stresses by careful attention to tolerances. Misaligned parts should not be forced into place. Where surface tensile stresse
23、s cannot be avoided, consider techniques like shot peening, surface rolling, or thermal stress relief to reduce undesirable stresses. When using thermal treatments for stress relief, consideration also needs to be given to the effect of time at elevated temperature on the properties of the product.
24、Heat treat weldments after welding. To avoid stress-corrosion cracking while the product is in the W temper, parts should be stored in a dry environment for as short a time as possible before artificial aging. Quenching causes desirable surface compressive stresses and undesirable internal tensile s
25、tresses. This should be considered when machining the parts. Use heat treating specifications that require process controls, (e.g., AMS 2770, 2771, 2772) for solution heat treating and overaging treatments as applicable.4.2 Die Forgings 4.2.1 Grain Flow Die design should be such as to preclude exces
26、sive grain run-out at the parting line and to avoid re-entrant grain flow at any point in the forging. 4.2.2 Heat Treatment Solution heat treatment should be accomplished when the part is as close to finished machine size as practicable. Preferably, the forging envelope should closely approximate th
27、e machined part envelope to preclude the need for excessive machining after heat treatment. Quenching from the solution temperature should be performed in such a manner as to provide uniform cooling on all surfaces of the part. The quench medium temperature should be as high as possible, commensurat
28、e with maintaining satisfactory mechanical properties and general corrosion resistance. 4.2.3 Preservation Parts and parts in process, except those made of product alclad on both sides, should be coated with AMS 3065 compound, or equivalent, until such time as the final protective coating is applied
29、. SAE ARP823E Page 4 of 4 4.3 Additional Information 4.3.1 The following documents provide additional guidance in avoiding stress-corrosion cracking in high strength aluminum alloy structures. These publications will aid designers and material engineers to utilize the material in design and applicat
30、ion and to specify applicable process controls. (1) ASTM G 64, Classification of Resistance to Stress-Corrosion Cracking of High Strength Aluminum Alloys (2) NASA Document MSFC-STD-3029: Guidelines For The Selection Of Metallic Materials For Stress-Corrosion Cracking Resistance In Sodium Chloride En
31、vironments Materials, Processes, And Manufacturing Department Metallic Materials And Processing Group (3) Metallic Materials Property Data Sheets (MMPDS), (4) NBS Monograph 156, “Stress Corrosion-Cracking Control Measures”, by B.F.Brown, Chapter 4 on Aluminum Alloys, 1977 June. (5) MIL-HDBK-1568, Ma
32、terials and Processes for Corrosion Prevention and Control in Aerospace Weapons Systems 5. NOTES 5.1 The change bar ( l ) located in the left margin is for the convenience of the user in locating areas where technical revisions, not editorial changes, have been made to the previous issue of this document. An (R) symbol to the left of the document title indicates a complete revision of the document. PREPARED BY AMS COMMITTEE “D“
