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

At a Glance

Metadata	Details
Publication Date	2020-08-03
Journal	Materials
Authors	Oussama Chaieb, Oluwole A. Olufayo, Victor Songmené, Mohammad Jahazi
Institutions	École de Technologie Supérieure
Citations	5
Analysis	Full AI Review Included

Technical Analysis: MPCVD Diamond Solutions for Machining Hypereutectic Al-Si Alloys

6CCVD provides advanced Monocrystalline (SCD) and Polycrystalline (PCD) Chemical Vapor Deposition (CVD) diamond materials essential for high-performance tooling and metrology in aerospace and deep-space applications. This analysis connects the challenges identified in the research paper (“Investigation on Surface Quality of a Rapidly Solidified Al-50%Si Alloy Component for Deep-Space Applications”) directly to our core capabilities.

Executive Summary

This research highlights the critical need for ultra-hard, wear-resistant tooling when machining rapidly solidified (RS) hypereutectic Al-50%Si alloys for deep-space components (e.g., waveguide diplexers).

Application Focus: Machining high-silicon aluminum alloys for aerospace components requiring extremely tight tolerances and low surface roughness (target Sa < 0.8 µm).
Material Challenge: The high volume fraction of hard silicon grains (53%) makes the alloy highly abrasive, leading to rapid tool wear (flank wear, microchipping).
Tooling Used: Polycrystalline Cubic Boron Nitride (PCBN) tools coated with PVD Amorphous Diamond were employed to mitigate wear and adhesion.
Performance Achieved: The RS Al-50%Si alloy demonstrated superior surface roughness compared to conventional Al6061-T6 under optimized conditions.
Optimal Parameters: Best surface finish (minimal roughness) was achieved at low cutting speeds (76.2 m/min) and low feed rates (0.02286 mm/tooth).
Limitation Identified: Despite the diamond coating, tool life remains the primary constraint due to the extreme abrasiveness of the high-silicon matrix.
6CCVD Value Proposition: MPCVD Polycrystalline Diamond (PCD) offers a superior, bulk diamond solution for tooling inserts, providing maximum wear resistance and thermal stability necessary to overcome the tool life limitations observed.

Technical Specifications

Parameter	Value	Unit	Context
Workpiece Material	RS Al-50%Si	Alloy	Rapidly Solidified Hypereutectic Aluminum
Silicon Content	53	% Volume	Phase 1 (Silicon)
Target Roughness (Max)	0.8	µm (Sa)	Threshold for acceptable deep-space parts
Minimal Registered Roughness	0.743	µm (Sa)	Achieved with Tool 3 (3.175 mm)
Optimal Cutting Speed (Vc)	76.2	m/min	For minimal registered roughness
Optimal Feed Rate (Fz)	0.02286	mm/tooth	For minimal registered roughness
Hardness (BHN)	230	BHN	Brinell Hardness (RS Al-50%Si)
Thermal Conductivity	125	W/m-K	RS Al-50%Si
Tool Material/Coating	PCBN + Amorphous Diamond	PVD	Used to reduce wear and adhesion
Tool Diameter (T3)	3.175	mm	Tool yielding lowest attainable roughness
Vibration Threshold	120	m/min	Cutting speed above which high vibration occurs

Key Methodologies

The experimental design focused on optimizing milling parameters for surface quality while utilizing advanced tooling materials.

Material Synthesis: Rapidly Solidified (RS) hypereutectic Al-50%Si alloy was manufactured by melt-spinning, extrusion, and ultra-fast cooling (cooling rates 10⁴-10⁷ K/s) to achieve a fine-grain microstructure.
Tooling Strategy: Polycrystalline Cubic Boron Nitride (PCBN) end mills were selected and coated with Physical Vapor Deposition (PVD) Amorphous Diamond to enhance resistance against abrasive silicon particles.
Machining Setup: Milling tests were conducted on a HURON K2X10 CNC machine (28,000 RPM capacity) using a full factorial experiment plan.
Parameter Variation: Five levels of cutting speed (Vc), feed rate (Fz), and tool diameter (D) were tested, focusing on the effect of Vc and Fz on surface roughness.
Metrology: Surface roughness (Sa, Sq, Ssk, Sku, etc.) was measured using an OLYMPUS OLS4100 LEXT laser confocal microscope.
Dynamic Monitoring: An ICP® Triaxial Accelerometer was mounted on the workpiece to analyze the evolution of vibration as a function of cutting speed and feed rate.
Post-Process Analysis: Microstructural examination confirmed the absence of cracks or silicon grain tearing in the workpiece but identified significant flank wear and microchipping on the cutting tools.

6CCVD Solutions & Capabilities

The research confirms that machining high-silicon aluminum alloys requires tooling with extreme hardness and wear resistance, a requirement perfectly addressed by 6CCVD’s MPCVD diamond products. The PVD amorphous diamond coating used in the study is a good starting point, but the observed rapid tool wear necessitates a transition to bulk diamond materials for maximum tool life and consistent surface integrity.

Applicable Materials for Tooling and Metrology

Application Requirement	6CCVD Material Recommendation	Technical Justification
Extreme Wear Resistance	Polycrystalline Diamond (PCD)	MPCVD PCD offers superior bulk hardness and thermal stability compared to thin PVD coatings, drastically extending tool life against the abrasive 53% Si content.
Ultra-Precision Machining	Optical Grade SCD	For single-point diamond turning (SPDT) applications or ultra-precision metrology components, our SCD offers Ra < 1nm surface finish capability.
High-Frequency Components	Optical Grade SCD/PCD	Required for manufacturing the high-tolerance waveguide diplexers and microwave components mentioned, ensuring minimal insertion loss due to surface defects.

Customization Potential for Tooling Inserts

The study identified tool wear as the primary failure mechanism, necessitating frequent tool changes. 6CCVD provides the foundational material to create next-generation, highly durable diamond tooling inserts:

Custom Dimensions: We supply PCD plates and wafers up to 125mm in diameter, allowing tool manufacturers to maximize yield and produce large-format inserts.
Thickness Control: We offer PCD thicknesses from 0.1µm up to 500µm, providing flexibility for brazing onto PCBN or carbide substrates, or for creating robust, thick diamond cutting edges.
Laser Cutting Services: The paper utilized a 3.175 mm diameter tool (T3). 6CCVD offers in-house precision laser cutting and shaping services to produce custom PCD tool blanks, inserts, and complex geometries required for specialized end mills.
Ultra-Polishing: We guarantee polishing capabilities for PCD surfaces to Ra < 5nm (inch-size), ensuring the cutting edge geometry is optimized for the lowest possible surface roughness (Sa < 0.8 µm) on the workpiece.

Engineering Support

The relationship between cutting speed, feed rate, and vibration is complex, especially when dealing with novel materials like RS Al-50%Si.

Material Selection Expertise: 6CCVD’s in-house PhD team specializes in the mechanical and thermal properties of CVD diamond. We can assist tool designers and manufacturing engineers in selecting the optimal PCD grade and geometry for similar High-Silicon Aluminum Machining projects, maximizing tool life and minimizing vibration effects.
Thermal Management: Given the high thermal conductivity requirements of the aerospace components, our diamond materials offer superior heat dissipation, which is crucial for maintaining tool integrity and preventing thermal deformation during high-speed machining.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

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

Original Source

DOI: https://doi.org/10.3390/ma13153412

References

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