Effect of Mechanical Alloying Processparameters on Characteristics Ofai-B4cnanocomposite-Nanocrystllinepowder Particles

Highlights of the Study This study systematically investigated the effects of key mechanical alloying parameters—including milling time, milling speed, initial aluminum particle size, B₄C particle size, and B₄C content—on the morphological, particle-size, dispersion, and nanocrystalline characteristics of Al6061–B₄C composite and nanocomposite powders. The results demonstrated that optimization of mechanical alloying conditions can effectively control powder refinement, promote homogeneous incorporation of nanoscale B₄C into the aluminum matrix, and accelerate the formation of nanocrystalline Al structures. Key findings: 🟢 Processing-parameter evaluation: The effects of milling time (2–16 h), milling speed (320 and 420 rpm), initial Al particle size (21 and 71 μm), B₄C particle size (90, 700, and 1200 nm), and B₄C content (5 and 10 wt.%) were systematically investigated. 🟢 B₄C nanoparticle production: Nanosized B₄C particles with an average size of approximately 90 nm were successfully produced by milling commercially available 0.7 μm B₄C powder for 110 h. 🟢 Mechanical-alloying conditions: Al6061 and B₄C powders were mechanically alloyed for 2–16 h under an argon atmosphere using a ball-to-powder weight ratio of 20:1, with ethanol employed as the process control agent. 🟢 Morphological evolution: During the early stages of milling, soft aluminum particles were flattened because of plastic deformation, followed by extensive cold welding and subsequent fragmentation as milling progressed. 🟢 Cold-welding stage: After 2–4 h of milling, cold welding dominated the process, causing an increase in the average particle size and formation of flattened or laminated Al particles. 🟢 Fragmentation stage: Further milling progressively increased work hardening and promoted particle fracture, causing the average powder particle size to decrease. 🟢 Equiaxed morphology: After approximately 16 h of milling, a balance between cold welding and fragmentation resulted in the formation of relatively equiaxed aluminum powder particles. 🟢 Initial Al-size effect: Both 21 and 71 μm starting Al powders initially increased in particle size during milling, followed by progressive refinement at longer milling times. 🟢 Welding–fracturing equilibrium: The equilibrium between fracturing and cold welding was reached after approximately 10 h for the 21 μm Al powder and approximately 14 h for the coarser 71 μm powder. 🟢 Milling-speed effect: Increasing the milling speed from 320 to 420 rpm resulted in finer aluminum powder particles at any given milling time. 🟢 Accelerated particle refinement: At 320 rpm, the maximum particle size occurred after approximately 4 h, whereas increasing the speed to 420 rpm shifted this maximum to approximately 1.5 h, demonstrating faster fragmentation–welding–fragmentation cycles. 🟢 B₄C-content effect: Increasing B₄C content from 5 to 10 wt.% reduced the average Al–B₄C powder particle size at a given milling time. 🟢 Hard-particle milling effect: Because B₄C is substantially harder than aluminum, the reinforcement particles acted similarly to additional milling media, increasing the number of effective impacts and promoting Al particle fragmentation. 🟢 Work-hardening enhancement: Embedding fine B₄C particles into the aluminum matrix increased the work-hardening rate, further facilitating particle fracture and refinement. 🟢 Nanoparticle embedding: High-energy ball milling for approximately 8 h successfully embedded B₄C nanoparticles within flattened Al6061 particles. 🟢 Homogeneous reinforcement distribution: SEM imaging and elemental mapping demonstrated that milling broke up B₄C clusters and produced a relatively homogeneous distribution of the reinforcement within the aluminum matrix. 🟢 Al grain refinement: The crystallite size of monolithic aluminum decreased from approximately 160 nm to 80 nm after 8 h of milling at 320 rpm. 🟢 Higher-speed nanocrystallization: Increasing the milling speed to 420 rpm accelerated grain refinement, reducing the Al crystallite size to approximately 80 nm after only 4 h and to approximately 40 nm after 16 h. 🟢 B₄C-assisted nanocrystallization: Addition of B₄C nanoparticles accelerated the formation of a nanocrystalline aluminum structure, allowing an approximately 80 nm crystallite size to be achieved after only 4 h of milling. 🟢 Dislocation-mediated refinement: B₄C particles interacted with dislocations, increased dislocation density, and accelerated the grain-refinement process during mechanical alloying. 🟢 Optimal dispersion: Approximately 8 h of high-energy milling was sufficient to embed the ceramic nanoparticles and generate a homogeneous B₄C distribution within the Al6061 matrix. 🟢 Process-control capability: The results demonstrate that milling speed, milling duration, reinforcement concentration, and starting particle characteristics can be adjusted to control both powder particle size and Al crystallite size. Overall, the study demonstrates that careful optimization of mechanical alloying parameters provides effective control over the microstructural evolution of Al6061–B₄C nanocomposite powders. Increasing the milling speed from 320 to 420 rpm substantially accelerated particle fragmentation and nanocrystallization, while incorporation of B₄C promoted work hardening, dislocation accumulation, grain refinement, and homogeneous nanoparticle dispersion. An Al crystallite size of approximately 80 nm was achieved after 8 h of conventional milling, whereas increasing milling speed or incorporating B₄C nanoparticles reduced the time required to develop the nanocrystalline structure to approximately 4 h. These findings establish mechanical alloying as an effective processing route for producing uniformly reinforced Al–B₄C nanocomposite powders with controllable particle and crystallite characteristics. ARTICLE INFORMATION International Journal of Modern Physics B2008, Volume 22, Nos. 18 & 19, pp. 2924–2932 HOW TO CITE Khakbiz, M.; Akhlaghi, F. Effect of Mechanical Alloying Process Parameters on Characteristics of Al–B₄C Nanocomposite–Nanocrystalline Powder Particles. International Journal of Modern Physics B 2008, 22, 2924–2932. KEYWORDS Al–B₄C Nanocrystalline • Al Particle Size • Milling Time • Milling Speed • Mechanical Alloying • B₄C Nanoparticles • Al6061 • Nanocomposite