Skip to content
6CCVD Research

Investigation on Surface Quality of a Rapidly Solidified Al–50%Si Alloy Component for Deep-Space Applications

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2020-08-03
JournalMaterials
AuthorsOussama Chaieb, Oluwole A. Olufayo, Victor Songmené, Mohammad Jahazi
InstitutionsÉcole de Technologie Supérieure
Citations5
AnalysisFull AI Review Included

Executive Summary

Section titled “Executive Summary”

This research investigated the milling machinability and surface quality of a novel, rapidly solidified (RS) hypereutectic Al-50%Si alloy, specifically targeting high-performance deep-space applications.

  • Material Performance: The RS Al-50%Si alloy demonstrated improved overall surface roughness (Sa) measurements compared to the conventionally utilized Al6061-T6 alloy under similar cutting conditions.
  • Optimal Machining Parameters: To achieve the required surface integrity threshold (Sa < 0.8 µm), optimal parameters were identified: a low cutting speed (Vc) of 76.2 m/min and a low feed rate (fz) of 0.0241 mm/tooth (using the 3.175 mm diameter tool).
  • Critical Factor Identification: Cutting speed (Vc) was the most influential parameter, showing approximately 50% greater impact on surface roughness variation than the feed rate (fz).
  • Vibration Stability: The RS Al-50%Si alloy exhibited stable machining conditions with limited vibrations at cutting speeds below 120 m/min. Vibrations increased significantly only above Vc = 130 m/min.
  • Microstructural Integrity: Post-machining analysis confirmed that the alloy maintained its microstructural integrity, showing no evidence of delamination (cracks between Si grains and Al matrix) or tearing off of silicon grains.
  • Tooling Challenge: Machinability challenges were primarily associated with rapid tool wear (flank wear and microchipping) due to the high hardness and abrasive nature of the prominent silicon content (over 50%).
  • Tool Recommendation: Statistical analysis indicated that Tool 3 (3.175 mm diameter) provided the best balance of material removal rate and surface integrity for this alloy.

Technical Specifications

Section titled “Technical Specifications”
ParameterValueUnitContext
Material Composition (Volume)53 / 47% Si / % AlRapidly Solidified (RS) Hypereutectic Alloy
Density2.47g/cm3RS RSA-463 (Comparable Alloy)
Thermal Conductivity125W/m-KRS RSA-463 (Comparable Alloy)
Average Hardness (HRB)54 ± 4Rockwell Hardness BMeasured on RS Al-50%Si sample
Ultimate Tensile Strength (RM)230MPaExperimental result
Modulus of Elasticity (E)117GPaExperimental result
Percentage Elongation (A)0.94%Experimental result
Roughness Target (Max Sa)0.8µmAcceptable threshold for deep space parts
Optimal Cutting Speed (Vc)76.2m/minFor Sa < 0.8 µm (Tool 3)
Optimal Feed Rate (fz)0.0241mm/toothFor Sa < 0.8 µm (Tool 3)
Tool MaterialPCBNN/APolycrystalline Cubic Boron Nitride
Tool CoatingAmorphous diamondPVDUsed to reduce wear and adhesion
Critical Vibration Speed120m/minMachining stability limit for RS Al-50%Si
R-squared Prediction Accuracy (Sa)94.81%Statistical model accuracy for arithmetic roughness

Key Methodologies

Section titled “Key Methodologies”

The experimental study utilized a comprehensive approach combining material characterization, controlled milling tests, and detailed surface analysis:

  1. Material Manufacturing: The hypereutectic Al-50%Si alloy was produced using advanced Rapid Solidification (RS) techniques, specifically melt-spinning, extrusion, and ultra-fast cooling, to achieve a fine grain microstructure.
  2. Mechanical Characterization:
    • Hardness distribution was mapped across the sample using a Buehler hardness tester (Brinell and Rockwell B).
    • Tensile strength, yield strength, and elongation were determined following American Society for Testing and Materials (ASTM) E8 standards.
  3. Tooling: Polycrystalline Cubic Boron Nitride (PCBN) tools coated with Physical Vapor Deposition (PVD) amorphous diamond were selected to mitigate wear, adhesion, and particle diffusion. Five different tool diameters (D1) were tested.
  4. Milling Setup: Experimental milling tests were conducted on a HURON K2X10 CNC machine (28,000 RPM capacity).
  5. Experimental Design: A full factorial experiment plan was implemented, varying cutting speed (Vc) and feed rate (fz) across five levels, in addition to varying radial and axial depths of cut.
  6. Vibration Monitoring: An ICP Triaxial Accelerometer (AT401-3) was mounted on the workpiece (back-to-back comparison method) to measure vibration amplitude (Vy) along the X, Y, and Z axes.
  7. Surface Roughness Analysis:
    • Roughness was measured using an OLYMPUS OLS4100 LEXT laser confocal microscope over a millimeter square area.
    • 3D areal roughness parameters (Sa, Sq, Sp, Sv, Sz, Ssk, Sku) were calculated and compared against Al6061-T6 results.
  8. Statistical Modeling: Analysis of Variance (ANOVA) was performed on transformed roughness data (Sa and Sq) to identify significant parameters and generate power form regression equations for roughness prediction.
  9. Microstructural Inspection: Microscopic observations were performed on the machined surface and the cutting tool to evaluate microstructural defects (delamination, Si tearing) and wear mechanisms (flank wear, microchipping).

Commercial Applications

Section titled “Commercial Applications”

The unique combination of high silicon content, low CTE, and high strength achieved through Rapid Solidification makes this alloy and its optimized machining process suitable for demanding engineering sectors:

  • Deep Space and Satellite Technology:
    • Manufacturing of intricate, high-precision components such as waveguide diplexers and microwave components.
    • Essential for parts requiring extremely low thermal expansion to maintain dimensional stability across vast temperature fluctuations in space.
  • Radio Frequency (RF) Networks:
    • Production of precision microwave components (1 to 90 GHz) where internal polished waveguide surfaces are necessary to achieve low insertion losses and minimize conductor loss due to surface roughness.
  • High-Performance Aerospace:
    • Applications requiring light-weight alloys with improved mechanical properties, high strength, and excellent wear resistance, exceeding the performance of conventional 6061-T6 and 7075-T6 alloys in specific thermal environments.
  • Automotive Industry:
    • Components requiring high thermal conductivity and wear resistance, including cylinder heads, engine blocks, clutch housings, and compressors.
View Original Abstract

To meet the requirements for high-performance products, the aerospace industry increasingly needs to assess the behavior of new and advanced materials during manufacturing processes and to ensure they possess adequate machinability, as well as high performance and an extensive lifecycles. Over the years, industrial research works have focused on developing new alloys with an increased thermal conductivity as well as increased strength. High silicon content aluminum (Al-Si) alloys, due to their increased thermal conductivity, low coefficient of thermal expansion, and low density, have been identified as suitable materials for space applications. Some of these applications require the use of intricate parts with tight tolerances and surface integrity. These challenges are often tied to the machining conditions and strategies, as well as to workpiece materials. In this study, experimental milling tests were performed on a rapidly solidified (RS) Al-Si alloy with a prominent silicon content (over 50%) to address challenges linked to material expansion in deep space applications. The tests were performed using a polycrystalline cubic boron nitride (PCBN) tool coated with amorphous diamond to reduce tool wear, material adhesion, surface oxidation, and particle diffusion. The effects of cutting parameters on part surface roughness and microstructure were analyzed. A comparative analysis of the surface with a conventionally utilized Al6061-T6 alloy showed an improvement in surface roughness measurements when using the RS Al-Si alloy. The results indicated that lower cutting speed and feed rate on both conventional and RS Al-Si alloys produced a better surface finish. Reduced vibrations were also identified in the RS Al-Si alloy, which possessed a stable cutting time at low cutting speeds but only displayed notable vibrations at cutting speeds above 120 m/min.

Tech Support

Section titled “Tech Support”

Original Source

Section titled “Original Source”

References

Section titled “References”
  1. 2017 - Assessment of circumferential cracks in hypereutectic Al-Si clutch housings [Crossref]
  2. 2003 - An overview of the development of Al-Si-Alloy based material for engine applications [Crossref]
  3. 1983 - Machining and Machinability of Aluminum Cast Alloys [Crossref]
  4. 1999 - Machinability of graphitic metal matrix composites as a function of reinforcing particles [Crossref]
  5. 2008 - Effect of Si content on turning machinability of Al-Si binary alloy castings [Crossref]
  6. 2016 - Effect of silicon content on machinability of Al-Si alloys [Crossref]
  7. 2017 - Effect of Si content on the microstructure and properties of Al-Si alloys fabricated using hot extrusion [Crossref]

Reads Similar to This

Wide-field Planar Magnetic Imaging Using Spins in Diamond Lossless Phonon Transition Through GaN‐Diamond and Si‐Diamond Interfaces Raman lasers for trace gas detection (Conference Presentation)