Research on the Wear Resistance of Aluminum Powder Metallurgical Materials: The Influence of Load and Sliding Speed on the Wear Mechanism

Aluminum powder metallurgical materials are widely used in wear-resistant scenarios such as automotive parts and bearings due to their lightweight and design flexibility. However, their wear resistance is significantly affected by load conditions and sliding speed. Revealing the regulatory laws of the two on the wear mechanism is the key to optimizing material formulations and service parameters.

1、 Basic classification of wear mechanisms and load effects

The wear process of aluminum powder metallurgical materials follows a composite mechanism of abrasive wear, adhesive wear, and fatigue wear, and load changes directly change the dominant mode:

Low load zone (<20 MPa)

Wear characteristics: mainly abrasive wear, with micro convex bodies on the sliding surface cutting each other, producing small abrasive chips (particle size<10 μ m).

Mechanism analysis: When the load is small, the surface oxide film (Al ₂ O3) of the material is not completely broken, and the abrasive particles mainly come from surface processing residual particles or environmental invasion impurities. For example, under the conditions of a load of 10 MPa and a sliding speed of 0.5 m/s, the wear rate of pure aluminum powder metallurgical specimens is about 5 × 10 ⁻⁶ mm ³/N · m, and parallel shallow scratches can be seen on the worn surface.

Material response: Fine grain strengthening (grain size<10 μ m) and uniform distribution of hard points (such as Al ₂ O Ⅲ nanoparticles) can effectively hinder abrasive particle penetration, reducing wear rate by 30% -50%.

Medium to high load zone (20-100 MPa)

Wear characteristics: The synergistic effect of adhesive wear and fatigue wear results in local stress at the contact interface exceeding the material yield strength, leading to metal transfer and microcrack initiation.

Mechanism analysis: When the load exceeds the critical value (about 25 MPa), the oxide film ruptures, and the exposed metal comes into direct contact to form adhesive nodes. After the node fractures, sheet-like debris (particle size 50-200 μ m) is generated. At the same time, cyclic contact stress induces subsurface plastic deformation, forming fatigue cracks that propagate to the surface, leading to block like peeling. For example, under a load of 60 MPa and a speed of 2 m/s, the wear rate of Al-10Si alloy increases to 2 × 10 ⁻⁴ mm ³/N · m, and fatigue striations and adhesive tear marks can be seen on the fracture surface.

Material response: Adding 3% -5% Cu or Ni to form hard and brittle intermetallic compounds (such as Al ₂ Cu) can improve the anti adhesion ability; Introducing a 0.5% graphite solid lubricant, the friction coefficient is reduced from 0.3 to 0.15 through a "self-lubricating film", resulting in a decrease of over 40% in wear rate.

2、 The regulation law of sliding speed on wear behavior

Low speed zone (<1 m/s)

Limited thermal effect: Friction generates less heat, wear is mainly mechanical cutting, wear surface temperature<100 ℃, oxidation can be ignored.

Speed sensitive feature: The increase in speed leads to an increase in the frequency of abrasive particle contact, resulting in a linear increase in wear rate. For example, the wear rate of pure aluminum is 8 × 10 ⁻⁶ mm ³/N · m at a speed of 0.2 m/s, and increases to 3 × 10 ⁻⁵ mm ³/N · m when it reaches 0.8 m/s.

High speed zone (>1 m/s)

Thermomechanical coupling dominates: Friction generates heat, leading to an increase in surface temperature (up to 200-300 ℃), softening of the aluminum matrix, and a shift in wear mechanism towards oxidative wear and thermal fatigue wear.

Typical phenomenon: When sliding at high speed, a loose Al ₂ O3 oxide layer is formed on the surface, which is prone to peeling off and forming debris; At the same time, thermal cycling causes surface cracking, forming a "thermal fatigue wear zone". For example, at a speed of 3 m/s and a load of 80 MPa, the wear rate of Al-20% Al ₂ O3 composite material reaches 5 × 10 ⁻⁴ mm ³/N · m, with a surface oxide film thickness of 10-20 μ m and accompanied by a network of microcracks.

Critical speed threshold: For materials with different compositions, there is a critical speed at which the wear mechanism undergoes a transition (such as approximately 1.5 m/s for Al-5Mg alloy), beyond which the wear rate significantly increases.

3、 Multi factor coupling model of wear mechanism

In actual working conditions, load and velocity jointly affect wear behavior through contact stress (σ=P/A) and sliding kinetic energy (E=0.5mv ²), and the following correlation can be established:

Low load and low speed: The wear is mainly caused by abrasive wear, and the wear rate is linearly related to the load, followed by the influence of speed.

Medium load speed: Adhesive wear dominates, and the wear rate is proportional to the square root of the speed and the square of the load.

High load and high speed: Oxidative wear and thermal fatigue dominate, and the wear rate is controlled by temperature exponential functions (such as the Arrhenius equation). The synergistic effect of load and speed causes the wear rate to increase exponentially.

Material optimization strategy:

Low load condition: Adopting fine grain and hard point strengthening (such as nano SiC particles) to improve surface hardness (HV ≥ 150).

High load and high-speed operating conditions: Design a "anti-wear heat dissipation" composite structure, such as surface gradient distributed graphite (dense inner layer, porous outer layer containing oil), while introducing high thermal conductivity phases (such as Cu particles) to reduce temperature rise.