J. An

Improvement of the wear behavior of stircast Al-Si-Pb alloys by hot extrusion

Abstract The wear behavior of as-cast and hot extruded Al–Si–Pb alloys were investigated under dry conditions using a pin-on-disc type wear testing machine. The results show that the microstructure and mechanical properties can be greatly improved and porosity can be significantly decreased by hot extrusion. These factors contribute to great increase in wear resistance of hot extruded Al–Si–Pb alloys. Optical observation and X-ray photoelectron spectroscopy (XPS) analysis reveal the almost constant wear rate at mediate load levels. Better resistance to seizure for Al–Si–Pb alloys with more than 15 wt% lead are due to a film of lubricant covering almost the entire worn surface. This film is a mixture of different constituents containing Al, Fe, Si, O and Pb.

Effect of Si on the interfacial bonding strength of Al–Pb alloy strips and hot-dip aluminized steel sheets by hot rolling

Abstract Bonding of Al–Pb alloy strips and hot-dipped Al or Al–2% Si steel sheets were carried out using hot rolling. The effects of addition of 2% Si to the bath, the dipping time, the thickness of the intermetallic layers and the fraction of the blank interfaces on the bonding strength are investigated. In all case, two different kinds of interfaces are produced, hot-dip aluminized steel sheets and Al–Pb alloy strips are bonded through the mechanism of blank and block interface bonding. The total bonding strength depends mainly on that of blank interface and the fraction of the blank interfaces. The bonding strength of blank interfaces is four or five times as high as that of block interfaces. There is a linear relationship between the bonding strength and the fraction of the blank interfaces. An EPMA linescan across the blank interface reveals that higher concentration of aluminum in the transition layer of Fe and Al formed in the blank interface region for a dipped specimen of Al–2% Si than that for a dipped specimen of Al.

Hot-roll bonding of Al-Pb bearing alloy strips and hot dip aluminized steel sheets

In this paper, the basic bonding mechanism between two materials of practical importance is identified. One of the materials is carbon steel, which has been aluminized on its surface by immersion in molten aluminum. This step produced a Fe-Al intermetallic compound layer. The other material is an Al-Pb alloy (a bearing material). The two materials were hot roll bonded together. It was found that the Fe-Al intermetallic compound broke into discontinuous blocks during the hot rolling operation. The block of intermetallic compound remained bonded to the steel. The overall bond between the Al-Pb strip and the steel strip resulted from two different bonds. The Al-Pb strip and the Fe-Al intermetallic compound (this is called the “block bond” in this paper) and the Al-Pb strip and the bare steel surface in the area where the block separated from the steel substrate (this is called the “blank bond” in this paper).The effects of dipping time and thickness of the intermetallic layer as well as the fractional amount of blank interfaces on the interfacial bonding strength were investigated. The total bonding strength mainly depended on that of blank interfaces and the area fraction of blank interfaces. There was a linear relationship between total bonding strength and fraction of blank interfaces. The bonding strength of blank interfaces was four times as high as that of the block interfaces. The fraction of blank interfaces increased with increasing intermetallic thickness values below 73 µm and decreased beyond 73 µm.

Mechanism of bonding of Al–Pb alloy strip and hot dip aluminised steel sheet by hot rolling

Abstract Specimens of Al–Pb bearing alloy strip and hot dip aluminised steel sheet with intermetallic layers of various thicknesses have been successfully bonded by hot rolling. It was found that during hot rolling, two different kinds of interfaces were produced. The hot dip aluminised steel sheets and Al–Pb alloy strips were observed to bond by a mechanism of blank and block interface bonding. The effects that the dipping time, the thickness of the intermetallic layers, and the fraction of blank interfaces had on the interfacial bonding strength were investigated. The total bonding strength was found to depend mainly on the bonding strength and fraction of blank interfaces. The bonding strength of blank interfaces was four times as high as that of block interfaces. The fraction of blank interfaces increased with increasing thicknesses of the intermetallic layer up to a thickness of 73 µm and decreased with increasing values of thickness above 73 µm. There was a linear relationship between bonding strength and fraction of blank interfaces.

Hot roll bonding of Al–Pb-bearing alloy strips and steel sheets using an aluminized interlayer

Abstract This article describes a study of the application of a hot roll bonding technique to Al–Pb-bearing alloy strips and steel sheets using an aluminized interlayer. It was found that the overall bond between these two metals resulted from two different types of bonds: a “block” bond, linking the Al–Pb alloy strips and aluminum topcoat layer to the Fe–Al intermetallic compound, and a “blank” bond, linking the Al–Pb alloy strips and aluminum topcoat layer to the bare steel surface in the area where the block has separated from the steel substrate. The study investigated the effects of dipping time on the thickness of the intermetallic layers and of the area fraction of blank bond on the bond strength. The overall bond strength depends mainly on the strength and the area fraction of the blank bond. A linear relationship exists between the overall bond strength and the area fraction of blank bond. The bond strength of the blank bond is four times greater than that of the block bond. The area fraction of the blank bond increases with increasing intermetallic thickness up to a thickness of 73 μm, but thereafter decreases due to the rotation of the intermetallic blocks.

Friction and wear characteristics of Mg–11Y–2·5Zn magnesium alloy treated by laser surface melting

Abstract An attempt has been made to enhance the tribological properties of Mg–11Y–2·5Zn alloy by laser surface melting with a 6 kW continuous wave CO2 laser processing system. The microstructure and microhardness of the surface layer on Mg–11Y–2·5Zn alloy were characterised using X-ray diffractometer, laser microscopy and Vickers hardness indentation. The laser surface melted zone consisted of fine dendrites and coarse dendrites growing epitaxially from the liquid/solid interface. Microhardness was improved from 69–70 HV for the substrate to 77–83 HV for the fine dendritic microstructure. The friction and wear characteristics were investigated using a pin on disc apparatus. The coefficient of friction curve of the laser surface melted specimen was similar to that of the untreated specimen. Laser surface melted Mg–11Y–2·5Zn alloy exhibited good wear resistance, which has been explained by refinement of microstructure in the melted zone. Four wear mechanisms including abrasion, delamination, thermal softening and melting, have been observed.

An Investigation on Subsurface Microstructural Evolution and Mild to Severe Wear Transition in AZ51 Magnesium Alloy

The wear behavior of as-cast AZ51 alloy was investigated using a pin-on-disc configuration within a load range of 20–380 N and a sliding speed range of 0.1–4.0 m/s under dry sliding conditions. The coefficient of friction and wear rate were measured as a function of applied load at various sliding speeds. Morphologies and chemical compositions of worn surfaces were analyzed for determination of wear mechanisms using scanning electron microscope (SEM) and energy-dispersive X-ray spectrometry (EDS). Microstructural evolution, plastic deformation, and hardness of the subsurfaces as well as worn surface hardness were characterized by confocal scanning laser microscopy and hardness testing for the establishment of a corresponding relationship between microstructural evolution and mild to severe wear transition in AZ51 alloy. The results show that there exists a strong relationship between wear behavior and subsurface microstructural evolution; that is, surface oxidation and strain hardening originating from plastic deformation of the microstructure prevail in mild wear regime, whereas thermal softening with dynamic recrystallization (DRX) in subsurface and surface melting dominate in severe wear regime. With increasing load and sliding speed to certain critical states, the friction-induced heat accumulation activates DRX in subsurface and surface melting successively, leading to a rapid rise in wear rate and typical worn surface morphology with extruded edges or multilayered structure edges. The mild to severe wear transition is determined to be controlled by initiation of DRX in the subsurface of AZ51 alloy.

Friction and wear characteristics of hot-extruded leaded aluminum bearing alloys

The friction and wear characteristics of hot-extruded Al-Pb alloys with lead contents in the range 0–25 wt.% and as-cast Al-Pb alloys with lead content of 20 wt.% were investigated under dry-sliding conditions using a pin-on-disc test machine. It was found that hot extrusion greatly decreased the porosity that was caused by powerful stirring and considerably improved the mechanical properties of stircast Al-Pb alloys, including wear behavior. The coefficient of friction and wear rate decreased with increasing lead content, and especially the antiseizure property of hot-extruded Al-Pb alloys containing 20 wt.% and 25 wt.% lead were improved remarkably. Optical observation revealed that the reason for this was the formation of a black compact film of lubricant that covered almost the entire worn surface of specimens at a highly applied load level. This film is a mixture of different constituents containing Al, Fe, Si, O, and Pb.

Microstructure and dry sliding wear behavior of hot-extruded AlSiCuPb bearing alloys

The microstructures, mechanical properties and dry wear behavior of hot-extruded AlSiCuPb bearing alloys have been studied. It showed that the hot-extruded AlSiCuPb alloys possessed microstructures with uniformly distributed lead particles and fine broken grains of silicon, and exhibited further improved mechanical properties in comparison to the stir cast ones. With increasing the lead content, the wear rate decreased greatly and wear rate-load curves took different form for extruded bearing alloys containing 20% and 25% lead. Optical observation revealed the reason was formation of a black compact film of lubricant covering almost the entire worn surface of specimens at highly applied load level. This film is a mixture of different constituents containing the elements Al, Si, O, Fe and Pb.

Comparative studies on wear behaviour between as cast AZ91 and Mg97Zn1Y2 magnesium alloys

Abstract The wear behaviour of as cast magnesium alloys, Mg97Zn1Y2 and AZ91, was investigated under dry conditions in load ranges of 20–380 and 20–240 N respectively, using a pin on disc wear testing machine. The microstructure, thermal stability and elevated temperature tensile properties were characterised by optical microscopy, X-ray diffraction, differential thermal analysis and tensile testing respectively. The wear behaviour can be divided into three successive phases in terms of surface temperature induced by frictional heat, i.e. ambient temperature to eutectic temperature or precipitate dissolution temperature, eutectic temperature or precipitate dissolution temperature to the liquidus temperature and above the liquidus temperature. The Mg97Zn1Y2 alloy exhibited good wear resistance compared with the AZ91 alloy for applied loads in excess of 80 N, which has been explained in terms of thermal stability of the intermetallic phase and elevated temperature mechanical properties of the two materials tested, by surface temperature analysis and subsurface observation.