1、 WORLDWIDE ENGINEERING STANDARDS Test Procedure GMW16867 Determine Permanent Growth Potential in Aluminum Due to Metallurgical Instability Copyright 2012 General Motors Company All Rights Reserved December 2012 Originating Department: North American Engineering Standards Page 1 of 8 1 Scope Note: No
2、thing in this standard supercedes applicable laws and regulations. Note: In the event of conflict between the English and domestic language, the English language shall take precedence. 1.1 Purpose. The standard described herein measures the potential for aluminum to experience permanent growth due t
3、o metallurgical instability. Aluminum parts often operate at temperatures that facilitate phase transformation and precipitation of supersaturated alloying elements. These metallurgical changes may be accompanied by volumetric expansion. Background on this phenomenon is given in Appendix A. Results
4、of a benchmark study are presented in Appendix B. 1.2 Foreword. Summary of test method: Ten right-circular cylinders with premeasured end-to-end lengths are heated at 250 C for 100 h. After cooling to ambient temperature, each sample is remeasured with the change in length converted into percent (%)
5、 growth. Average and standard deviation(s) growth are calculated. Mean + 3s growth is defined herein as “Maximum Permanent Growth Potential” for the material and rated per Section 5.4 against a maximum allowance. 1.3 Applicability. Aluminum alloys. 2 References Note: Only the latest approved standar
6、ds are applicable unless otherwise specified. 2.1 External Standards/Specifications. ISO 10360-2 2.2 GM Standards/Specifications. None 2.3 Additional References. Boileau, J.M.,C.A. Cloutier, L.A. Godlewski, P.A. Reeber-Symanksi, C. Wolverton, J.E. Allison, “The Dimensional Stability of Cast 319 Alum
7、inum,” SAE paper 2003-01-0822. Hunsicker, H.Y. “Dimensional Changes in Heat Treating Aluminum Alloys,” Met. Trans. A, v. 11A, p. 759 (1980). Li, M., R. Vijayaraghavan, C. Wolverton, J.E. Allison, “Simulation of Local Microstructures and Thermal Growth of a Cast 319 Aluminum Alloy component,” Proceed
8、ings 1st International Symposium on Metallurgical Modeling for Aluminum Alloys, ASM International, 2003. 3 Resources 3.1 Facilities. A temperature-controlled room where measurements will be made. 3.2 Equipment. 3.2.1 Coordinate Measuring Machine (CMM) with temperature compensation and 3-dimensional
9、length-measurement uncertainty 2.50 m calibrated per ISO 10360-2 or its successor. 3.2.2 Convection oven with temperature control capability of 250 C 5 C. 3.2.2.1 Capability may be established by measuring and recording the furnace temperature with a thermocouple co-located with the samples. Copyrig
10、ht General Motors Company Provided by IHS under license with General Motors CompanyNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-GM WORLDWIDE ENGINEERING STANDARDS GMW16867 Copyright 2012 General Motors Company All Rights Reserved December 2012 Page 2 of 8 3.3 Te
11、st Vehicle/Test Piece. Material for test shall be taken from parts made by a documented process in a defined level of development or production. 3.4 Test Time. Not applicable. 3.5 Test Required Information. Not applicable. 3.6 Personnel/Skills. Proficiency in programming and operating CMM equipment.
12、 4 Procedure 4.1 Preparation. Machine 10 test samples into right-circular cylinders per Figure 1. If sufficient material is unavailable, alternate geometries are acceptable per agreement by GM. Place a permanent reference mark on each specimen surface for use in orienting the specimen during length
13、measurement. Number each specimen. 4.2 Conditions. 4.2.1 Environmental Conditions. Laboratory air. 4.2.2 Test Conditions. Deviations from the requirements of this standard shall have been agreed upon. Such requirements shall be specified on component drawings, test certificates, reports, etc. 4.3 In
14、structions. 4.3.1 Dimensional Measurements. Program a CMM conforming to paragraph 3.2.1 to measure temperature-compensated end-to-end length of the test specimens. Measurements are made before and after the thermal conditioning in paragraph 4.3.1.5. Figure 1: Specimen Dimensions, and Tolerances Note
15、: (A) = Centers of both ends are located by CMM scans. (B) = Best planes describing both ends are found with radius scans. Figure 2: CMM Details 4.3.1.1 Use the same CMM and probe for all measurements, and locate specimens in the same position on the bed. Use the reference marks on each specimen to
16、establish a common orientation. 4.3.1.2 Stabilize specimens at the CMM ambient temperature. Attach the CMM temperature probe to each sample and compensate for workpiece temperature. Use a Coefficient of Thermal Expansion (CTE) value of 21 x 10-6/C (or other appropriate value). 4.3.1.3 End-to-End Len
17、gth. Locate the centers of the specimen ends and determine their best planes by scanning them at radius, A and B in Figure 2. Determine end-to-end length as the distance between the best planes at the centers of the ends. 4.3.1.4 Thermal Conditioning. Place samples into a preheated furnace and hold
18、at 250 C 5 C for 100 h ( 2 h). Cool samples with forced air (e.g., a fan). B A A 0 . 0 1 0 C 0 . 0 2 0 B 0 . 0 1 0 C 0 . 0 2 0 1 0 0 10 C C 0 . 0 2 0 C 0 . 0 1 0 D a t u m: C y l i n d r i c a l s u r f a c e C D i m e n s ion s in mm D i m e n s ion a l t o ler a n c e 0 . 1 e x c e p t a s n o t e
19、 d S u r f a c e f i n i s h R A 3 . 2 m C e n t e r mar k s 0 . 2 5 d i a . may r e mai n o n e n d s Copyright General Motors Company Provided by IHS under license with General Motors CompanyNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-GM WORLDWIDE ENGINEERING
20、 STANDARDS GMW16867 Copyright 2012 General Motors Company All Rights Reserved December 2012 Page 3 of 8 4.3.1.5 Post-Treatment Measurements. Recondition samples at ambient temperature and repeat measurements in paragraphs 4.3.1.3 and 4.3.1.4. 5 Data 5.1 Calculations. Growth calculation: Determine me
21、an and standard deviation of growth calculated by: %100 in itia lin itia lfin a lGr o w t h l ll% 5.2 Interpretation of Results. The Maximum Permanent Growth Potential is defined herein as the result of mean + 3s for the 10 samples tested. 5.3 Test Documentation. The process and development/producti
22、on level shall be documented for the origin of samples tested. Include all initial and final sample lengths, initial and final measurement temperature, percent (%) Growth for each sample, and the Maximum Permanent Growth Potential per paragraph 5.2. 5.4 Evaluation and Rating. 5.4.1 Acceptance. The m
23、aterial may be reported as substantially free from potential permanent growth if the Maximum Permanent Growth Potential defined in paragraph 5.2 is less than 0.020%. 5.4.2 Other criteria for acceptability may be dictated by GM. 6 Safety This standard may involve hazardous materials, operations, and
24、equipment. This standard does not propose to address all the safety problems associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. 7 Notes 7.1 Glossar
25、y. Maximum Permanent Growth Potential. Defined herein as the largest value of mean+3s of the sample groups tested per this standard. 7.2 Acronyms, Abbreviations, and Symbols. CMM Coordinate Measuring Machine CTE Coefficient of Thermal Expansion DC Die Casting FEA Finite Element Analysis GSSLT Global
26、 Subsystem Leadership Team s Standard Deviation 8 Coding System This standard shall be referenced in other documents, drawings, etc., as follows: Maximum permanent growth potential per GMW16867: 0.020% 0.020% or alternate acceptance criterion Test procedure standard number Copyright General Motors C
27、ompany Provided by IHS under license with General Motors CompanyNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-GM WORLDWIDE ENGINEERING STANDARDS GMW16867 Copyright 2012 General Motors Company All Rights Reserved December 2012 Page 4 of 8 9 Release and Revisions T
28、his standard was originated in October 2012. It was first approved by the Non Ferrous Metals and Castings GSSLT in December 2012. It was first published in December 2012. Issue Publication Date Description (Organization) 1 DEC 2012 Initial publication. Copyright General Motors Company Provided by IH
29、S under license with General Motors CompanyNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-GM WORLDWIDE ENGINEERING STANDARDS GMW16867 Copyright 2012 General Motors Company All Rights Reserved December 2012 Page 5 of 8 Appendix A: Background on Permanent Growth in
30、Aluminum A1 Summary of Phenomenon Many alloying elements (e.g., Cu, Mg, Si) have increased solubility in aluminum at elevated temperatures. During and after cooling from solidification or solution treatment these alloying elements precipitate from solid solution as fine particles. Since the density
31、of the precipitates differs from the aluminum solid solution, dimensional change also occurs. Elements such as Cu, Mg, and Si form precipitates that result in permanent growth. A complicating phenomenon concerns how rapidly the elements precipitate. Precipitation is rapid between 275 C and 425 C, sl
32、owing exponentially as the temperature reduces. Precipitation at room temperature may occur at an imperceptible pace (thousands of hours). Unprecipitated alloying elements that remain in supersaturated solid solution have the potential for later precipitation upon reheating to operating temperatures
33、 (for example, in automotive engines), where consequent growth may occur in tens of hours. In addition, precipitates undergo transformation from one structure to another during aging. Such precipitate evolution also contributes to growth. The most reliable method to stabilize the microstructure agai
34、nst permanent growth is by aging until alloying elements no longer remain in supersaturated solid solution and precipitates no longer evolve. Heat treatment of Al-Si-Cu-Mg alloys that concludes with aging at 230 C to 240 C for 3 h to 5 h (e.g., T7) has been shown to minimize the maximum growth poten
35、tial to below 0.020%. Aging treatments at lower temperatures (e.g., the T6 temper and some T5 tempers) may not completely stabilize the microstructure. The permanent growth that does occur can exceed 0.1%. While this may be small compared to thermal expansion, the latter is predictable through stand
36、ard Finite Element Analysis (FEA) and is commonly accommodated in early design. Permanent growth due to precipitation and precipitate evolution depends strongly on prior thermal processing and may not manifest itself during prototype development. Precipitation and precipitate evolution occur more ra
37、pidly in the hotter regions of a part and more slowly in the cooler sections. In automotive cylinder blocks this can cause differential growth leading to bore distortion. The overall part may grow, complicating stack-up tolerancing. A2 Risk Factors in Unstable Microstructures A2.1 Prior thermal hist
38、ory of a part may not be controlled sufficiently during part manufacture to eliminate all possibility of future permanent growth. A2.2 Thermal processing may change between prototype, production ramp-up, and regular production due to differences in equipment and queuing times. A2.3 Pre-production pa
39、rts may not represent the entire spectrum of thermal histories possible in a process. Hence, the potential for permanent growth may escape detection during prototype and validation. A2.4 Thermal exposure during durability testing may not reproduce the events leading to detrimental permanent growth d
40、uring customer usage. A2.5 Failure due to permanent growth is not consistent. Successful experience with parts produced by a particular process for one design may not apply to another. A2.6 Changing heat treatment to remedy permanent growth may adversely affect mechanical properties. This is not eas
41、ily managed late in product design. Copyright General Motors Company Provided by IHS under license with General Motors CompanyNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-GM WORLDWIDE ENGINEERING STANDARDS GMW16867 Copyright 2012 General Motors Company All Right
42、s Reserved December 2012 Page 6 of 8 Appendix B: Verification of Test Method B1 Summary The potential for permanent growth was determined on Al-Si-Cu-Mg aluminum cylinder blocks, one bedplate and one cylinder head spanning tempers from F (as-cast), T4 (solution treated and air quenched), T5 (aged on
43、ly), and T7 (solution treated and aged). Soak times at 250 C of 1 h and 10 h were studied in addition to the 100 h time specified herein. Aging at 220 C reduced Maximum permanent growth potential to less than 0.020%. Substantial growth potential remained after all other heat treatments, including a
44、T5 age at 190 C for 8 h. B2 Sample Preparation Samples were extracted from bulkheads of cylinder blocks and bedplates, and deck faces of cylinder heads, all of Al-Si-Cu-Mg aluminum alloy, and mostly prepared by production processing. In one case cylinder blocks were solution treated and quenched a T
45、4 condition; half of them were subsequently aged to T7; permanent growth potential was thus compared for T4 and T7. In another case, die cast blocks of Al-Si-Cu alloy were subjected to various T5 aging treatments; the permanent growth potential was compared between T5 and F (as-cast). B2.1 Dimension
46、al Measurements. Samples were mounted on the bed of a Zeiss Prisma 7 CMM, Figure B1. The specimens were measured before and after heat treatment per the requirements listed under paragraph 4.3. B3 Thermal Conditioning Samples were divided into three loosely wired groups and placed in a convection fu
47、rnace held at 250 C 5 C. The groups were removed at 1 h, 10 h, and 100 h. The data represent a long-term study samples from different parts were treated at different times. B4 Dimensional Results. The growth data is shown in Figure B2 and summarized in Table B1. B5 Conclusion The maximum permanent g
48、rowth potential for Al-Si-Cu and Al-Si-Cu-Mg alloys is below 0.020% when the material has been aged above 220 C. Materials in the F (as-cast) and T4 conditions exhibit maximum permanent growth potentials on the order of 0.1%. Copyright General Motors Company Provided by IHS under license with Genera
49、l Motors CompanyNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-GM WORLDWIDE ENGINEERING STANDARDS GMW16867 Copyright 2012 General Motors Company All Rights Reserved December 2012 Page 7 of 8 Figure B1: Measurement Setup, Specimen Horizontally Fixtured on CMM Bed Note: Various Die Casting (DC) T5 data have been
