The mild–severe wear transition of aluminum alloys is considered evidence that the wear changes from a stable state to an unstable state, which is of great importance in engineering applications. The purpose of this study is to evaluate the mild–severe wear transition of the 2195 Al–Li alloy for different loads and to elucidate the causes behind it. To this end, dry sliding tribometric tests were carried out by varying the normal load from 2 to 40 N at room temperature. The results show that the change in wear rate can be divided into three distinct stages, including weak growth at low load (2–4 N), rapidly increased growth at medium load (8–16 N), and gradually increased growth at high load (32–40 N). The transition from mild to severe wear is observed at loads ranging from 4 to 8 N. Characterization of the worn surface of the Al–Li alloy via scanning electron microscopy shows that abrasion and oxidation are the dominant wear phenomena in the mild wear regime. On the other hand, delamination, adhesion, and severe plastic deformation become dominant in the severe wear regime. The reason for the occurrence of the transition is the tribo-induced plastic deformation of the substrate.

/pdf/dry-sliding-wear-behavior-and-mild-severe-wear-transition-of-3cyjw9yb.pdf

Dry Sliding Wear Behavior and Mild–Severe Wear Transition of the AA2195-T6 Alloy under Different Loads

This study examined the influence of the rotational speed of an A356 aluminum alloy consumable rod on thermo-mechanical issues, microstructure, and the wear resistance of coating during friction surfacing on an AA2024 aluminum alloy. The study utilized a comprehensive experimental-numerical analysis to fulfill its objectives. The findings reveal that the width and thickness of the coating increase by 7 and 18 % percent, respectively, as the rotational speed of the consumable rod is augmented from 600 to 800 revolutions per minute (rpm). A higher rotational speed of the consumable rod facilitates plastic deformation of the material within it, enabling softer material to be deposited on the substrate's surface under reduced axial force. Simulation outcomes display that the maximum plastic strain is experienced on the coating's upper surface, which contacts the tip of the consumable rod. Upon moving toward the interface between the coating and the substrate, the degree of plastic strain rapidly diminishes. In the coatings produced by rotational speeds of 600 and 800 rpm, a fine grain layer forms on the upper side of the coating that comes into contact with the consumable rod's tip. Friction surfacing utilizing a rotational speed of 800 rpm, a traverse speed of 125 mm/min, and an axial feeding rate of 100 mm/min, results in increases of 9 and 38 percent in hardness and wear resistance respectively, compared to the AA2024 substrate. 

Combined experimental-numerical analysis of A356 aluminum alloy friction surfacing on AA2024 aluminum alloy substrate

Investigation of the effect of traverse speed in friction surfacing of Al–16Si alloy by smoothed-particle hydrodynamics (SPH) simulation and experimental study

Using the smoothed-particle hydrodynamics (SPH) simulation method and experimental investigation, this study evaluated the effect of consumable rod axial feeding rate on microstructure, mechanical properties, and wear resistance of coatings during the friction surfacing process of an AlSi alloy containing 16.6 wt% silicon on a commercial grade pure aluminum substrate. The interaction of coating and substrate at the interface was investigated using the thermomechanical simulation. According to simulation and experimental results, by increasing the axial feeding rate from 100 to 150 mm/min, the average deposition efficiency has increased from 36 to 43 %. The predicted results achieved from smoothed-particle hydrodynamics simulation show that by increasing the axial feeding rate from 100 to 150 mm/min, the shear stress at the coating/substrate interface increases from 86 ± 4 to 112 ± 6 MPa. By considering the average velocity at the interface, the simulation predicted the roughness with high precision. By increasing the axial feeding rate from 100 to 150 mm/min, interface roughness decreased from 105.2 ± 29.7 to 83.2 ± 26.9 μm. Compared to the pure aluminum substrate, surfacing with an AlSi alloy containing 16.6 wt% silicon results in minimum/maximum hardness and wear resistance increases by 212 / 265 % and 57 / 60 %, respectively. 

Experimental and numerical investigation of Al 16Si alloy friction surfacing on AA1050 aluminum substrate: Effect of axial feeding rate

In this work, Al alloys with 6.6%, 10.4%, and 14.6% Si were deposited as thick coatings by Friction Surfacing (FS), resulting in grain refinement and spheroidization of needle-shaped eutectic Si phase. Lubricated sliding wear tests were performed on a pin-on-disc tribometer using Al-Si alloys in as-cast and FS processed states as pins and 42CrMo4 steel discs. The chemical composition of the worn surfaces was analyzed by X-ray photoelectron spectroscopy (XPS). The wear mechanisms were studied by scanning electron microscopy (SEM) and focused ion beam (FIB), and the wear was evaluated by measuring the weight loss of the samples. For the hypoeutectic alloys, spheroidization of the Si phase particles in particular leads to a significant improvement in wear resistance. The needle-shaped Si phase in as-cast state fractures during the wear test and small fragments easily detach from the surface. The spherical Si phase particles in the FS state also break away from the surface, but to a smaller extent. No reduction in wear due to FS was observed for the hypereutectic alloy. Here, large bulky primary Si phase particles are already present in the as-cast state and do not change significantly during FS, providing high wear resistance in both material states. This study highlights the mechanisms and limitations of improved wear resistance of Si-rich Al alloys deposited as thick coatings by Friction Surfacing.

/pdf/effects-of-microstructure-modification-by-friction-surfacing-1tx2uksn.pdf

Malte R. Schütte

Papers

Effects of Microstructure Modification by Friction Surfacing on Wear Behavior of Al Alloys with Different Si Contents