ANALYSIS OF MAGNESIUM ADDITION, HYDROGEN POROSITY AND T6 HEAT TREATMENT EFFECTS ON MECHANICAL AND MICROSTRUCTURAL PROPERTIES OF PRESSURE DIE CAST 7075 ALUMINUM ALLOY

This paper summary is based on the article "Analysis of Magnesium Addition, Hydrogen Porosity and T6 Heat Treatment Effects on Mechanical and Microstructural Properties of Pressure Die Cast 7075 Aluminum Alloy" presented at the THE GRADUATE SCHOOL OF NATURAL AND APPLIED SCIENCES OF MIDDLE EAST TECHNICAL UNIVERSITY

1. Overview:

• Title: ANALYSIS OF MAGNESIUM ADDITION, HYDROGEN POROSITY AND T6 HEAT TREATMENT EFFECTS ON MECHANICAL AND MICROSTRUCTURAL PROPERTIES OF PRESSURE DIE CAST 7075 ALUMINUM ALLOY
• Author: ECE ALAT
• Publication Year: SEPTEMBER 2012
• Publishing Journal/Academic Society: THE GRADUATE SCHOOL OF NATURAL AND APPLIED SCIENCES OF MIDDLE EAST TECHNICAL UNIVERSITY
• Keywords: 7075, tensile strength, flexural strength, hydrogen porosity, T6 heat treatment, pressure die casting.

2. Research Background:

• Social/Academic Context of the Research Topic: "Aluminum alloys are having more attention due to their high specific stiffness and processing advantages. 7075 aluminum alloy is a wrought composition aluminum alloy in the Al-Zn-Mg-Cu series. Due to the significant addition of these alloying elements, 7075 has higher strength compared to all other aluminum alloys and effective precipitation hardenability characteristic."
  "On the other hand, aluminum alloys have some drawbacks, which hinder the widespread application of them. One of the most commonly encountered defects in aluminum alloys is the hydrogen porosity. Additionally, in case of 7075, another problem is the lack of fluidity."
• Limitations of Existing Research: Not explicitly mentioned in the paper.
• Necessity of the Research: "Magnesium addition is thought to be effective in compensating this deficiency. Accordingly, in this study, die cast 7075 aluminum alloy samples with hydrogen porosity and additional magnesium content were investigated."

3. Research Purpose and Research Questions:

• Research Purpose: "The aim was to determine the relationship between hydrogen content and hydrogen porosity, and the effects of hydrogen porosity, additional magnesium and T6 heat treatment on ultimate tensile and flexural strength properties of pressure die cast 7075 aluminum alloy."
• Key Research Questions: Not explicitly mentioned in the paper as questions, but implied in the research purpose.
• Research Hypotheses: Implied hypotheses are:
  • Magnesium addition affects fluidity and mechanical properties of die cast 7075 aluminum alloy.
  • Hydrogen content is related to hydrogen porosity in die cast 7075 aluminum alloy.
  • Hydrogen porosity, magnesium addition, and T6 heat treatment influence the ultimate tensile and flexural strength of pressure die cast 7075 aluminum alloy.

4. Research Methodology

• Research Design: Experimental research to investigate the effects of magnesium addition, hydrogen porosity, and T6 heat treatment. "pressure die casting was conducted at two stages. In the first stage, 7075 aluminum alloy with an increase in magnesium concentration was melted and secondly 7075 aluminum alloy was cast directly without any alloying addition."
• Data Collection Method: "7075 aluminum alloy returns were supplied from a local pressure die casting company. After spectral analysis, pressure die casting was conducted at two stages… While making those castings, hydrogen content was measured continuously before each casting operation. As a final operation T6 heat treatment is carried out for certain samples. Finally, in order to accomplish our aim, mechanical and microstructural examination tests were conducted."
• Analysis Method: "mechanical and microstructural examination tests were conducted." Mechanical tests included "tensile test, flexural strength" and "hardness test". Microstructural examination included "Optical Microscopy" and "Image Analysis".
• Research Subjects and Scope: Pressure die cast 7075 aluminum alloy samples with varying magnesium content and hydrogen porosity, with and without T6 heat treatment.

5. Main Research Results:

• Key Research Results:
  • "As the magnesium content increased, tensile and flexural strength values slightly diminished."
  • "As hydrogen content increased, hydrogen porosity increased linearly. This relationship was found to be as: Hydrogen porosity % = 3.0325 x hydrogen content + 0.4006"
  • "As hydrogen content increased, hydrogen porosity increased, and eventually, tensile and flexural strength values diminished."
  • "Blistering decreases the heat treatment effect on mechanical properties."
• Statistical/Qualitative Analysis Results: Statistical and qualitative results are presented in figures and tables throughout Chapter 4 and Appendices. For example, "Table 11. Magnesium Concentration and UTS Values." and "Figure 39. Graph that shows the Relationship between Hydrogen Content and Hydrogen Porosity % for 7075."
• Data Interpretation: Increased magnesium content slightly decreased mechanical strength. Increased hydrogen content led to increased hydrogen porosity and decreased mechanical strength. T6 heat treatment improved strength but blistering reduced the effectiveness of T6 treatment.
• Figure Name List:
  • Figure 1. Alloy Series in Wrought Aluminum Alloys [1].
  • Figure 2. The Binary Phase Diagram of Al-Zn Alloy [1].
  • Figure 3. Al- Mg-Zn Ternary Phase Diagram, Liquidus Projection [1].
  • Figure 4. Al- Mg-Zn Ternary Phase Diagram, Solidus Projection [1].
  • Figure 5. Solubility of Hydrogen in Aluminum at 1 atm Hydrogen Pressure [1].
  • Figure 6. Porosity as a Function of Hydrogen Content in Sand-Cast Aluminum and Aluminum Alloy Bars [1].
  • Figure 7. Ultimate Tensile Strength versus Hydrogen Porosity for Sand-Cast Bars of Three Aluminum Alloys [1].
  • Figure 8. Influence of Gas Content on the Tensile and Yield Strengths of Aluminum Alloy 356 [1].
  • Figure 9. Key Components of Modern Cold Chamber Die Casting Machine from Operator Side [11].
  • Figure 10. Key Components of Modern Cold Chamber Die Casting Machine from Top View [11].
  • Figure 11. Cold Chamber [11].
  • Figure 12. Effect of Heat Treatment on 7075 [9].
  • Figure 13. Artificial Ageing Curves for 2024-T4 Sheet [29].
  • Figure 14. Four Precipitation Sequence of Al-Zn-Mg-Cu Alloys [29].
  • Figure 15. Alloy 7075-O Sheet, Annealed, 500X [1].
  • Figure 16. Experimental Procedure Flowchart.
  • Figure 17. Induction Furnace Front View.
  • Figure 18. Induction Furnace Top View.
  • Figure 19. Hyscan II Hydrogen Content Measurement Equipment.
  • Figure 20. Schematic of Component Layout.
  • Figure 21. HIDROTEKNIK MEP200 HPDC Machine.
  • Figure 22. Die Assembly Containing Tensile and Three Point Bending Test Specimens.
  • Figure 23. PQ2 Diagram that is drawn for the dedicated mold and high pressure die casting machine. Red dotted line represents optimal operating parameter set for phase II [34].
  • Figure 24. Chamber.
  • Figure 25. T6 Heat Treatment.
  • Figure 26. Heat Treated Samples.
  • Figure 27. Resistance Furnace.
  • Figure 28. Foundry Master UV Vacuum CCD Spectrometer Equipment.
  • Figure 29. Mares 50 Tonnes Hydraulic Tensile Test Machine.
  • Figure 30. Three Point Bending Test Specimens.
  • Figure 31. Three Point Bending Test Specimen Dimensions.
  • Figure 32. Metacut-M 250 Cut-Off Machine.
  • Figure 33. Samples that are cut for Metallographic Examination.
  • Figure 34. Forcipol 2V Grinder-Polisher Instrument.
  • Figure 35. SOIF XJP - 6A Optical Microscope.
  • Figure 36 Magnesium Composition versus UTS.
  • Figure 37. Magnesium Composition versus Flexural Strength.
  • Figure 38. Distinguishment between Hydrogen Gas and Shrinkage Porosity.
  • Figure 39. Graph that shows the Relationship between Hydrogen Content and Hydrogen Porosity % for 7075.
  • Figure 40. Hydrogen Porosity % vs Ultimate Tensile Strength (MPa).
  • Figure 41. Picture of a Tensile Test Specimen after Fracture.
  • Figure 42. Picture of a Tensile Test Specimen after Fracture.
  • Figure 43. Hydrogen Content versus Flexural Strength.
  • Figure 44. Blistering on T6 Heat Treated 7075 Sample.
  • Figure 45. Blistering and Hardness Test Indentation.
  • Figure 46. The Grain Structure of Pressure Die Cast 7075, 100X.
  • Figure 47. Hydrogen Porosity at the Gate Exit of the Sample 3-13.
  • Figure 48. Hydrogen Porosity at the Runner of the Sample 3-13.
  • Figure 49. Gate Exit and Runner Hydrogen Porosity Analysis Comparison.
  • Figure A. 1. Microstructure Test Report for Sample 2-1 (7075+Mg), 100X.
  • Figure A. 2. Microstructure Test Report for Sample 2-2 (7075+Mg), 100X.
  • Figure A. 3. Microstructure Test Report for Sample 2-3 (7075+Mg), 100X.
  • Figure A. 4. Microstructure Test Report for Sample 2-4 (7075+Mg), 100X.
  • Figure A. 5. Microstructure Test Report for Sample 2-5 (7075+Mg), 100X.
  • Figure A. 6. Microstructure Test Report for Sample 3-1 (7075), 100X.
  • Figure A. 7. Microstructure Test Report for Sample 3-3 (7075), 100X.
  • Figure A. 8. Microstructure Test Report for Sample 3-4 (7075), 100X.
  • Figure A. 9. Microstructure Test Report for Sample 3-5 (7075), 100X.
  • Figure A. 10. Microstructure Test Report for Sample 3-7 (7075), 100X.
  • Figure A. 11. Microstructure Test Report for Sample 3-8 (7075), 100X.
  • Figure A. 12. Microstructure Test Report for Sample 3-10 (7075), 100X.
  • Figure A. 13. Microstructure Test Report for Sample 3-11 (7075), 100X.
  • Figure A. 14. Microstructure Test Report for Sample 3-13 (7075), 100X.
  • Figure A. 15. Microstructure Test Report for Sample 3-14 (7075), 100X.
  • Figure A. 16. Microstructure Test Report for Sample 3-16 (7075), 100X.
  • Figure A. 17. Microstructure Test Report for Sample 3-17 (7075), 100X.
  • Figure A. 18. Microstructure Test Report for Sample 3-18 (7075), 100X.
  • Figure A. 19. Microstructure Test Report for Sample 3-19 (7075), 100X.
  • Figure A. 20. Microstructure Test Report for Sample 3-20 (7075), 100X.
  • Figure B. 1. Three Point Bending Test Report for the First Seven 7075+Mg Samples.
  • Figure B. 2. Three Point Bending Test Report for the 2-x Identified 7075+Mg Samples.
  • Figure B. 3. Three Point Bending Test Report for the 7075 Samples

6. Conclusion and Discussion:

• Summary of Main Results: "As the magnesium content increased, tensile and flexural strength values slightly diminished… As hydrogen content increased, hydrogen porosity increased linearly… As hydrogen content increased, hydrogen porosity increased, and eventually, tensile and flexural strength values diminished… Blistering decreases the heat treatment effect on mechanical properties."
• Academic Significance of the Research: The study provides quantitative data on the effects of magnesium addition and hydrogen porosity on the mechanical properties of pressure die cast 7075 aluminum alloy. It also highlights the linear relationship between hydrogen content and porosity.
• Practical Implications: The findings suggest that while magnesium addition might improve fluidity, it can negatively impact mechanical strength in die cast 7075 alloy. Controlling hydrogen content is crucial to minimize porosity and maintain mechanical properties. Blistering during T6 heat treatment needs to be addressed to maximize the benefits of heat treatment.
• Limitations of the Research: "Shrinkage porosity values were not constant. For that reason, they were unable to be prevented. Eventually, they disturbed the dense structure and caused degradation of some of the samples." The study acknowledges the difficulty in controlling shrinkage porosity, which could have influenced the results.

7. Future Follow-up Research:

• Directions for Follow-up Research: "In high pressure die casting operations, gating design effect should also be considered… Accordingly, hydrogen porosity at the runner should also be evaluated, in addition to the hydrogen porosity analysis from casting products." Future research should investigate the influence of gating design on porosity and optimize casting parameters to minimize shrinkage porosity and blistering.
• Areas Requiring Further Exploration: Further exploration is needed to fully understand the interaction between magnesium addition, hydrogen porosity, shrinkage porosity, and blistering on the mechanical properties of die cast 7075 aluminum alloy.

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9. Copyright:

• This material is "ECE ALAT"'s paper: Based on "ANALYSIS OF MAGNESIUM ADDITION, HYDROGEN POROSITY AND T6 HEAT TREATMENT EFFECTS ON MECHANICAL AND MICROSTRUCTURAL PROPERTIES OF PRESSURE DIE CAST 7075 ALUMINUM ALLOY".
• Paper Source: Not available in the document.

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