Due to differences in material properties (such as hardness, strength, and ductility), application scenarios (such as high reliability requirements in aerospace and 3C products), and shot peening objectives (such as improving fatigue resistance and optimizing surface smoothness), there are significant differences in the performance requirements for ceramic beads among different types of metal workpieces. The following is a specific analysis based on common types of metal workpieces:
###1, Aluminum alloy workpieces: focus on "mild impact+surface protection"
The characteristics of aluminum alloys (such as aircraft body components and 3C product phone/computer casings) are low hardness (HB30-150), good ductility, and surface deformation or scratches due to excessive impact. The core goal of shot peening is to form effective residual compressive stress while avoiding excessive surface damage. Therefore, the requirements for ceramic beads are focused on:
-Fine particle size: Typically, ceramic beads with a particle size of 80-200 mesh (diameter of approximately 75-180 μ m) are chosen. Fine particle size can reduce the "chiseling" effect on the aluminum surface, avoid deep scratches or local plastic deformation, and ensure surface smoothness (lower Ra value), meeting the aesthetic requirements of 3C product shells.
-Moderate hardness: The hardness of ceramic beads should be controlled within HRC 55-65 (Mohs hardness 8-8.5). If the hardness is too high (such as exceeding HRC 70), it is easy to cause microcracks on the aluminum surface; If it is too low, it cannot effectively form a plastic deformation layer, which affects the anti fatigue effect.
-* * More regular shape * *: Priority should be given to ceramic beads with high sphericity and no edges (such as roundness ≥ 0.8) to avoid local stress concentration caused by irregular particles during impact and prevent "overspray" damage (such as dents and peeling) on the surface of aluminum alloy.
###2, Titanium alloy workpieces: balancing "strength matching+anti pollution"
The characteristics of titanium alloys (such as aircraft engine blades and spacecraft structural components) are high strength (tensile strength up to 900-1400MPa), low thermal conductivity, and easy surface oxidation. Shot peening needs to meet both the requirements of "sufficient impact force to form residual compressive stress" and "avoiding the introduction of impurity pollution". The requirements for ceramic beads are:
-* * Density and kinetic energy matching * *: Select ceramic beads with a density higher than the upper limit (3.85-3.90g/cm ³). Titanium alloy has high strength and requires higher kinetic energy impact to produce effective plastic deformation on the surface layer; But the density needs to be lower than that of steel shot (to avoid lattice distortion caused by excessive impact), and higher than that of glass shot (to ensure sufficient kinetic energy).
-High purity and low breakage rate: Titanium alloys require extremely high surface cleanliness (especially in the aerospace industry), and ceramic beads need to use high-purity raw materials (such as zirconia toughened alumina) to reduce impurities (such as iron and silicon); At the same time, it is necessary to have high impact strength (≥ 3.5MPa) and reduce the breakage rate - if the ceramic beads are broken, the fragments may embed into the surface of the titanium alloy, causing subsequent corrosion or fatigue cracks.
-Particle size adaptation component size: For small precision components (such as titanium alloy bolts), choose 60-100 mesh fine-grained ceramic beads to avoid excessive impact; For large structural components such as fuselage frames, a coarser particle size of 40-60 mesh can be selected to improve shot blasting efficiency.
###3, Stainless steel workpieces: emphasizing "high impact force+wear resistance"
The characteristics of stainless steel (such as gears and pressure vessels) are high hardness (HB150-300) and high toughness. The goal of shot peening is to form a deep residual compressive stress layer on the surface through strong impact to resist fatigue failure under alternating loads. The requirements for ceramic beads focus on:
-* * High hardness and wear resistance * *: The hardness of ceramic beads needs to reach HRC 65-70 (Mohs hardness of 8.5 or above) to ensure effective "engraving" into the stainless steel surface (to avoid ceramic beads being "popped open" due to high stainless steel hardness); At the same time, it is necessary to have high wear resistance (wear rate ≤ 0.05%/hour), reduce particle size attenuation caused by long-term shot peening, and ensure consistency in batch processing.
-Coarse particle size and concentrated distribution: Ceramic beads with a diameter of 250-850 μ m (20-60 mesh) are usually selected, and the particle size distribution deviation should be ≤ 5%. Coarse grain size can provide a larger impact area and kinetic energy, ensuring that the stainless steel surface produces a plastic deformation layer with sufficient depth (≥ 0.1mm); Concentrated distribution avoids surface stress distribution disorder caused by uneven particle size.
-Slightly "angular" in shape: Compared to aluminum alloy, stainless steel can accept slightly angular ceramic beads (roundness 0.7-0.8), which enhance the "cutting effect" during impact by utilizing slight edges, accelerate the plastic flow of surface metal, and improve the stability of residual compressive stress.
###4, High temperature alloy workpieces: focus on "stability+resistance to high temperature pollution"
High temperature alloys (such as aviation engine turbine blades and rocket engine combustion chambers) are used in high-temperature (600-1000 ℃) and high-pressure environments for a long time, and their surfaces need to have resistance to high-temperature oxidation and thermal fatigue. Shot peening should avoid introducing thermally unstable impurities. The requirements for ceramic beads are:
-High temperature resistance and chemical stability: Ceramic beads should be made of high temperature resistant materials (such as zirconia based ceramics), with a melting point of ≥ 2000 ℃, and should not undergo chemical reactions with high-temperature alloys at high temperatures (such as avoiding the formation of low melting point compounds between silicon oxide in ceramic beads and nickel and chromium in alloys).
-Low porosity and high strength: High temperature alloy shot peening often uses higher spraying speeds (≥ 80m/s), and ceramic beads need to have low porosity (≤ 0.5%) and high bending strength (≥ 400MPa) to prevent powder from breaking under high-speed impact. If the powder adheres to the surface of the high-temperature alloy, it will form a thermal barrier during subsequent high-temperature service, affecting component heat dissipation.
###5, Light alloy small parts in the 3C field (such as magnesium alloy and zinc alloy shells): ultimate "precision+surface smoothness"
The light alloy small parts of 3C products, such as phone frames and laptop casings, require extremely high surface accuracy (Ra ≤ 0.8 μ m) and good material ductility (easy to deform). The goal of shot peening is "micro plastic deformation+non-destructive beautification". The requirements for ceramic beads are:
-* * Ultra fine sub micron particle size * *: Typically, 200-400 mesh (diameter 38-75 μ m) ultrafine ceramic beads are selected, and some even use micron sized (5-20 μ m) particles to form uniform residual compressive stress on the surface through "flexible impact", while avoiding leaving visible impact marks to the naked eye.
-* * Excellent sphericity * *: Ceramic beads need to be close to a perfect spherical shape (roundness ≥ 0.95), with a smooth and burr free surface, ensuring "point contact" rather than "line/surface contact" when in contact with the workpiece, to prevent scratching the surface of the light alloy (especially in the pre-treatment stage before anodizing, surface scratches will directly affect the final appearance).
###Summary: Core Difference Logic ceramic beads
The requirements of different metal workpieces for ceramic beads are essentially the matching logic of "workpiece characteristics shot peening target ceramic bead performance":
-Low hardness, high ductility workpieces (such as aluminum alloys, magnesium alloys) → require ceramic beads for "soft impact" (fine particle size, low hardness, high sphericity);
-High hardness, high-strength workpieces (such as stainless steel, titanium alloys) → require ceramic beads for "efficient impact" (high hardness, adaptable density, high wear resistance);
-Workpieces with high cleanliness and environmental adaptability (such as high-temperature alloys and aviation titanium alloys) require ceramic beads to be "stable and pollution-free" (high purity, low crushing rate, high temperature resistance).
This matching not only maximizes the shot peening effect (such as improving fatigue resistance by 30% -50%), but also reduces costs (such as reducing workpiece scrap rate and extending the service life of ceramic beads).
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