Piston Alloy Research Articles

Surface formation of plasma-electrolytic cobalt-containing coatings on piston alloys of aluminum

Based on the review of functional coatings on piston alloys of aluminum, a conclusion was made on the feasibility of using oxide coatings to increase the strength and durability of parts of the piston group of internal combustion engines. It is shown that the synthesis of the oxide layer on alloys of the Al-Si system (silumins) can be carried out by plasma electrolyte treatment in alkaline electrolytes with the addition of salts of dopant metals, in particular cobalt. This will allow to obtain coatings that have activity in the processes of catalytic combustion of fuel. It is proposed to form cobalt-containing oxide coatings on piston alloys by plasma-electrolytic oxidation in the electrolyte of 0.4 mol/dm3 K4P2O7, 0,1 mol/dm3 CoSO4 at current densities of 3–5 A/dm2 in the “decreasing power” mode. It is established that under these conditions during 15 min of oxidation on high-silicon alloys AL30 and AK21 an oxide layer with a content of up to 4.7 at.% Co is formed. The presence of up to 6.4 at.% of phosphorus in the synthesized coating will increase the heat resistance of the oxidized surface. At the same time, the silicon content in the surface layers decreases 4–5 times compared to the source material. It is shown that the morphology and phase composition of the coating changes with the incorporation of the additive component into its composition. The inclusion of cobalt occurs in the form of thermodynamically stable oxide Co3O4 (CoO·Co2O3), which crystallizes in the spinel crystal cell. This, along with a high degree of surface development is a prerequisite for improving the functional properties of the obtained oxide layers. The developed method was used for applying a cobalt-containing coating on the surface of a piston made of alloy AL30. It is established that in order to obtain a uniform oxide layer, certain technological parameters should be observed. The predicted use of a piston coated with cobalt-containing oxide coating will reduce the amount of toxic substances with exhaust gases and hourly fuel consumption, which is promising for intracylinder catalysis.

Morphological Evolutions of Ni-Rich Phases in Al-Si Piston Alloys during 250–400 °C Thermal Exposure Processes

The thermal stability of the Al-Si alloys during the thermal exposure process from 250 °C to 400 °C was systematically investigated. The relationships between the morphological evolution and the mechanical changes of the alloys were determined through the Vickers hardness test and materials characterization method. Initially, the alloys exhibited similar thermal degradation behavior. For example, the exposure process of the alloy at 300 °C can be divided into two stages according to the changes of the alloy hardness and the matrix micro-hardness. In detail, the first stage (0–2 h) exhibited a severe reduction of the alloy hardness while the second stage showed a more leveled hardness during the following 98 h. There are three identified morphological characteristics of Ni-rich phases in the alloy. Furthermore, the differences in both composition and the micro-hardness between these Ni-rich phases were confirmed. The underlying relationships between the morphological transformation of the Ni-rich phases and hardness fluctuation in the alloy were correlated and elucidated. The observed alloy hardness increase when the exposure temperature was 400 °C was unexpected. This behavior was explained from the perspectives of both Ni-rich phases evolution and dispersoid formation.

Effects of thermal exposure on the microstructure and mechanical properties of Al-12Si-4Cu-1Ni-1Mg-2Mn piston alloys

ABSTRACT The effect of thermal exposure on the elevated-temperature mechanical properties of heat-treated Al-12Si-4Cu-1Ni-1 Mg-2Mn piston alloys was investigated using optical microscopy (OM), scanning electron microscope (SEM), transmission electron microscopy (TEM), and tensile tests at elevated temperatures. The results showed that coarsening of the strengthening precipitates following a prolonged exposure at 350°C had a deleterious effect on the elevated-temperature tensile properties. Further thermal exposure up to 50 h did not result in even a slight reduction in the strength. After exposure at 350°C, the value of elevated-temperature ultimate tensile strengths of Al-12Si-4Cu-1Ni-1 Mg-2Mn piston alloys were 92, 80, and 73 MPa for 0 h, 10 h, and 100 h of thermal exposure, respectively, which are superior to those of the commercial piston alloys. The high-performance, elevated-temperature mechanical properties of Al-12Si-4Cu-1Ni-1 Mg-2Mn piston alloys can be attributed to the high thermal stability Mn-rich intermetallics and Al3CuNi.

Effect of thermal exposure on microstructure and high-temperature fatigue life of Al-Si piston alloys

A very effective approach is proposed here to increase the high-temperature fatigue life of an Al-Si piston alloy. Compared with traditional T6 heat treatment, the high-temperature fatigue life can be improved by three times of magnitude with thermal exposure treatment, which reduces the negative effects of gradually decreasing high-temperature fatigue life due to over-aging of piston durability. Specimens heat-treated by various processes have been tested in a rotating bending test machine under conditions of 50 MPa, 350 °C, and 80 Hz to observe the effects of thermal exposure on microstructure and high-temperature fatigue life. The thermal exposure treatment provides an effective method to optimize Si and the thermally stable phases of δ-Al3CuNi and γ-Al7Cu4Ni. It is one of the most important methods for improving the high- temperature fatigue life of an Al-Si piston alloy.

Experimental and computational study on thermo‐mechanical fatigue life of aluminium alloy piston

AbstractTo assess the life of a new diesel aluminium alloy piston under thermal shock loads, thermo‐mechanical fatigue (TMF) testing was conducted to characterise the TMF properties of the piston alloy, and an empirical model based on the constraint ratio concept was proposed to predict the TMF life of the piston. Considering that the empirical model required expensive experimental support, a platform with high‐frequency induction heating was established to simulate the force on the piston under thermal shock loads to calculate the piston life using the thermal shock test. Additionally, a finite element method was developed to compute the distributions of temperature, strain, and stress during this process. The characteristics of crack initiation and propagation in TMF test rods and piston mock‐ups were also investigated. The results showed that the TMF test rod suffered brittle fracture with brittle quasi‐cleavage features. The microcracks mainly occurred in primary Si particles due to stress concentration around the primary Si particles induced by the difference between the thermal expansion coefficients of Si and Al. From a macro perspective, the piston initially cracked at the rim above the pinhole, where the stress is larger than that along other directions. From a micro perspective, the protrusions of various sizes on the piston rim were induced by the compression stresses at high temperature. The piston cracks usually initiate around primary Si particles, propagate along the edge of primary Si in a straight line, bifurcate and then stop at a certain depth. If the piston was only heated, cracks or plastic deformations were not produced. The piston life can be assessed using the proposed empirical model based on the constraint ratio concept or thermal shock testing based on the developed platform. The difference between the predicted and experimental life was not greater than 7%.

Wear resistance mechanism of engine piston skirt coating under cold start condition

At the beginning of cold start, the lubricating oil temperature is low, the kinematic viscosity is high, the splash lubrication effect is poor, and the good lubricating oil film cannot be formed, therefore, the friction and wear between piston and cylinder is serious. In this paper, the wear mechanism of aluminum alloy piston skirt coating was studied in the cold start stage with severe wear degree: the dynamic simulation and cold start test analysis were carried out for the skirt with or without coating, and the wear morphology, knife pattern structure and friction force were compared, so as to determine the friction reduction energy efficiency of the coating in the cold start stage.

The effect of Ni-doping on the microstructure, hot deformation behavior, and processing map of as-cast Al–Si piston alloy

Al–Si alloy is widely utilized in automobile pistons and cylinders due to good castability, high strength-to-weight ratio, excellent thermal conductivity, good resistance to corrosion/oxidation, and acceptable wear resistance. To increase the efficiency of engine motor, it is imperative to modify and engineer the microstructure of Al–Si alloy to enhance the high-temperature behavior. For this reason, in the current study, different concentration of Ni (0.8% and 2%) was doped into Al–Si alloy during casting to generate various Ni-rich intermetallic compounds within the alloy matrix. AlNiCu, AlCu, AlFeSi, and Mg2Si were found to be the main intermetallic compounds precipitated within the dendritic and interdendritic regions, which could enhance the thermal stability and high-temperature performance. High-temperature compression test at high temperatures ranging from 400 to 550 °C and at different strain rates ranging from 10−3 to 1 s−1 was carried out to develop high-temperature processing map and optimize the hot workability parameters of Ni-doped Al–Si alloy. The maximum power dissipation efficiency (η) was observed within the temperature range of 450–500 °C and strain rate of 0.05–0.08 s−1 (lower strain rate) for Al–Si–0.8%Ni alloy and within the temperature range of 450–500 °C and strain rate of 0.3–1 s−1 (medium to high strain rate) for Al–Si–2%Ni alloy. Dynamic recrystallization was found to be the primary softening mechanism at high temperatures (T > 450 °C).

Aluminum Alloy Piston Fabrication Technology by Super Forging-KIRIU

This research aims to produce pistons a lighter and stronger piston, even in high compression and high engine speed conditions. The piston fabrication process is carried out by super forging using Aluminum as a raw material with a compound choice by Silicon or Magnesium. In addition, the outer layer of the piston is covered by molybdenum with the coating process as nanotechnology to prevent corrosion. Furthermore, the finishing is controlled by the programming system machine named CNC (Computerized Numerical Control). In addition to CNC, the automation system is carried out by the KIRIU machine which is also used in this study. The results of this study show that the use of Al-Si alloy base material has better piston quality and able to withstand high compression or high engine speed. Then, the Al-Si superforging piston compared to the two final automation processes of CNC and KIRIU. The evaluation results have proved that the KIRIU machine provides high accuracy and the actual production increases by 20% compared to CNC.

SELECTION OF CYLINDER-PISTON CLEARANCES OF ROTOR-PISTON ENGINES

The effect of the clearance amount of the cylinder-piston connection of the new design RPD-4.4/17.5 rotary-piston pneumatic engine on its performance and reliability is considered and analyzed. The clearance analysis was carried out taking into account the material from which the connecting pairs (piston and working cylinder) are made, and their operating temperature. In the first case, AK12M2MgN aluminum casting alloy was selected as a material for the manufacture of pistons of a rotary-piston pneumatic engine, and in the second case, cast iron with spherical graphite VCh 50 was selected. In both cases cast iron with spherical graphite HF 50 was selected as a material for manufacturing the working cylinder (actually, the rotor) of a rotary-piston pneumatic engine. The temperature change range was selected based on previous experimental studies of a prototype RPD-4.4/17.5 rotary piston pneumatic engine. Thus, the selected temperature range is from -25 to 100° C. The minimum temperature is due to the low temperature of the exhaust air in the pneumatic engine exhaust receiver, and the maximum is the temperature of the possible heating of the compressed air at the inlet to the inlet receiver of the pneumatic engine. Practical recommendations have been developed for choosing the optimal clearance of the cylinder-piston connection of the RPD-4.4/17.5 rotary-piston pneumatic motor and it has been found that the nominal end clearance, which ensures normal operation in the temperature range from -25...100° С, for a cast-iron piston and a cast-iron working cylinder is 25 microns, and for a variant of manufacturing a piston from an aluminum alloy - 33 microns. The proposed end clearances do not exceed the recommended values for similar connecting parts of such units. The correctness of the selected end clearances of the connecting parts has also been confirmed by bench tests of a prototype rotary piston pneumatic engine with subsequent fault finding of parts. It has been determined that a temperature increase of 100° C for an aluminum alloy piston manufacturing option results in a scuffing on the working cylinder surface, jamming of the piston followed by breakage of the movable links and damage to the piston bosses.

Influence of Ultrasonic Melt Treatment on Ni‐Containing Intermetallic Phases in Al–Si Piston Alloys

The influence of ultrasonic melt treatment (USMT) at different ultrasonic powers (0, 900, 2400, and 3000 W) on the morphology and chemical composition of Ni‐containing intermetallic phases (T‐Al9FeNi and δ‐Al3CuNi phases) in an Al‐11.5Si‐4Cu‐2Ni‐1Mg‐0.45Fe (wt%) piston alloy is investigated. The morphological characterization reveals that the USMT not only decrease the size of the T‐Al9FeNi and δ‐Al3CuNi phases but also change the morphology of T‐Al9FeNi from skeleton‐ to block‐shaped. The block‐shaped T‐Al9FeNi contributes the most to the high‐temperature properties because this morphology is beneficial in the formation of semi‐continuous network structures. The chemical composition of T and δ phases is analyzed. The Cu → Fe in the T phase and Ni ↔ Cu in the δ phase existing in the examined alloys are estimated. With increasing the ultrasonic power from 0 to 3000 W, the ultimate tensile strength, yield strength, and elongation are increased from 98.46 to 124.57 MPa, 82.4 to 101.87 MPa, and 2.95% to 5.12%, respectively, at 350 °C.

Evolution of surface roughness of a cast Al-Si-Cu piston alloy during thermal exposure

In the present work, samples of Al-Si-Cu piston alloy after T6 heat treatment were exposed for 2 h at temperatures ranging from 400 to 550 °C. The evolution of surface roughness and microstructure of the alloy during thermal exposure was studied by combination methods of roughness profiles, optical and scanning electron microscopy as well as XRD analysis. It is found that the roughness and mass of the alloy increase with the raise of the thermal exposure temperature, and the increasing rates of them are slow as the exposure temperature is below 500 °C, but accelerates abruptly when the temperature is higher than 500 °C. The variation of surface roughness of the alloy is closely related to phase transformation and oxidation during the thermal exposure.

Microstructure and Microhardness of Piston Alloy Al-10Si-2Cu Irradiated by Pulsed Electron Beam

Microstructure and Microhardness of Piston Alloy Al-10Si-2Cu Irradiated by Pulsed Electron Beam

Promising methods for strengthening piston aluminum alloys of heat engines

Due to the increase in the specific power of heat engines, one of the most pressing problems of modern engineering is the increase in the contact strength and heat resistance of piston aluminum alloys. The article considers the main promising methods of strengthening piston aluminum alloys in the aspect of modern technologies. Long-term operation of heat engines in operating conditions close to critical conditions contributes to melting of the grain boundaries of piston alloys, which negatively affects the reliability of internal combustion engines. In General, the task of increasing the heat resistance of piston aluminum alloys is one of the main tasks of modern engineering.

Effect of constraint factor on the thermo-mechanical fatigue behavior of an Al-Si eutectic alloy

The thermo-mechanical fatigue (TMF) behaviors and corresponding damage mechanisms of Al-Si piston alloy were investigated in the temperature range of 120~425 °C under different constraint factors (η). The TMF hysteresis loops exhibit asymmetrical, because the yield strength and elastic modulus decrease significantly with the increasing temperature. Taking the phase angles into consideration, the mean tensile stress for out of phase TMF (OP-TMF, η<0) and mean compressive stress for in-phase TMF (IP-TMF, η>0) can be found. The fatigue life of IP-TMF is longer than that of OP-TMF except for higher constraint factor, and the life of TMF decreases with the increasing absolute value of η. There are two different crack initiation mechanisms under the constrain TMF: primary phases broken mainly for OP-TMF and matrix deboned mainly for IP-TMF. The oxidation may have only little influence on the crack behavior and TMF life, considering the obvious damage by deboned or broken primary phases. The tensile stress is key factor for fatigue crack initiation and growth in primary phases (Si and intermetallic) under cyclic deformation. The TMF life under different constrain factors can be predicted by the strain energy model with good precision.

Optimization of Cutting Parameters for MRR, Tool Wear and Surface Roughness Characteristics in Machining ADC12 Piston Alloy Using DOE

Optimization of Cutting Parameters for MRR, Tool Wear and Surface Roughness Characteristics in Machining ADC12 Piston Alloy Using DOE

Surface integrity enhancement of ZL109 aluminum-silicon piston alloy employing the forward and reverse finish cutting method

The machined surface integrity has significance on fatigue life. The step-by-step feed cutting is put forward and adopted to machine ZL109 aluminum-silicon piston alloy. In addition, the forward and reverse finish cutting is also proposed to improve the machined quality and fatigue life. The result indicates that the step-by-step feed cutting can effectively avoid scratching and decrease surface roughness, bring about the compressive residual stress, and improve machined quality. Moreover, there is smaller elastic-plastic recovery and thermal expansion on the machined surface, when the step-by-step feed cutting is adopted, so that the machining dimension accuracy can be ensured perfectly. The forward and reverse finish cutting can effectively decrease the surface roughness and the tensile residual stress due to the thermal stress. So the larger the cutting thickness is, the smaller surface residual stress is, when the cutting depth is 0.15–0.30 mm in the forward and reverse finish cutting. It can improve the machined quality of ZL109 aluminum-silicon piston alloy and the fatigue life when the reasonable cutting parameter is adopted. Those results have an important practical significance.

Improved Elevated Temperature Properties in Al-13%Si Piston Alloys by Mo Addition

Eutectic Al-13%Si alloys are widely used in the automotive industry for manufacturing components, such as pistons and cylinder heads. To reduce greenhouse gas emissions and enhance the engine efficiency, their service temperature keeps increasing to 250-350 °C, leading to the deterioration of their mechanical properties and the creep resistance. In the present work, Mo was further added to Mn-containing Al-13%Si piston alloys aiming at improving the overall properties at elevated temperatures. Compared with the Mn-containing base alloy, Mo further enhanced the precipitation of dispersoids by expanding the dispersoid zone and restricting the dispersoid-free zone after the proper precipitation treatment (520 °C/12 h), resulting in a remarkable improvement in the yield strength at both room temperature and 300 °C, as well as the creep resistance at 300 °C. Furthermore, the beneficial effect of Mo addition on the improved yield strength and creep resistance was especially prominent during long-term thermal exposure (up to 1000 h at 300 °C) due to the synergistic effect of thermally stable dispersoids and the retardation of the gradual fragmentation and spheroidization of Si particles.

Temperature analysis of oxide coating of aluminum alloy piston used in diesel engine

The task of increasing in the efficiency (lowering of fuel consumption) of diesel engines is considered. The distribution of temperatures and stresses on the surface of oxide-coated piston coated by galvanic plasma modification is analized. The basic equations are obtained using the finite element method and solved using the ANSYS Workbench 18.1 and Solidworks 17. It is found thatthe surface temperature increases with increasing of coating thickness due to decrease in thermal outflow. The increase in maximum temperature relative to the uncoated piston is 64.3 % for 0.13 mm thickness coating. The temperature curves obtained for different thicknesses of the bottom are similar to each other and approximately equidistant. The numerical modeling showed that higher temperature in the combustion chamber is provided by thermal barrier coatings, which increases the efficiency of the engine. Lowering the surface temperature of the piston (substrate) creates favorable conditions for the piston to work.

Comparative analysis of different materials for piston and justification by simulation

The objective of this paper is stress distribution and thermal analysis of Aluminum and Magnesium alloy pistons. At room temperature, the strength of WE43A is lower than that of Al-7Si piston, but at elevated temperatures, WE43A can withstands more efficient due its mechanical and thermal properties than that of Al-7Si. After performing analysis, results in the form of graphs signify that total deformation in WE43A is directly proportional to an increase in pressure, due to which magnesium is a softer metal than the AL-7Si. Total heat flux of AL-7Si is lower than that of WE43A, thus magnesium alloy pistons perform much more efficient at higher temperature range.

Structure Modification upon Ultrasonic Processing of an AA4032 Piston Alloy: Comparison of Permanent Mold and Direct-Chill Casting

Piston Al-Si alloys have very complex compositions and multi-phase heterogeneous structure, so it is necessary to control the formation of primary and eutectic compounds. In this study, the ultrasonic melt processing (USP) of a eutectic Al-Si piston alloy (AA4032-type) was performed in a permanent mold and during direct-chill (DC) casting to study its effects on the structure refinement and modification. The principal difference between these two ways of casting is that in the permanent mold the solidification front progressively moves towards the ultrasound source, while in the DC casting the position of the solidification front is fixed in space. The results showed that the USP can successfully refine primary Si, Fe-containing intermetallics and aluminum grains. Refinement of primary Si was accompanied by the increase in its amount, which was attributed to both enhanced heterogeneous nucleation and fragmentation. The refinement of Fe-containing intermetallics and Al grains resulted from the fragmentation mechanism and were more pronounced when USP was applied below the liquidus temperature in the permanent mold. However, the eutectic phases coarsened upon USP, and this effect was most pronounced when USP was applied to the semi-solid material. This was related to the strong attenuation of acoustic waves, which effectively heats the semi-solid material and induces corresponding coarsening of the phases. Acoustic streaming induced by an oscillating sonotrode affected the depth of the sump while simultaneously decreasing the macrosegregation, which reflects the dominant role of the melt flow directed against natural convection. The results demonstrated the importance of the solidification stage at which the USP was applied and the specifics of the USP mechanisms acting at the different stages of solidification.