Search results

131A Aluminium Alloy Sand or Die Castings (suitable for Pistons, etc.).

PROBABLY one of the most remarkable features of our generation has been the ability of the metallurgist to produce alloys meeting the current needs of industry in providing the requisite mechanical characteristics, capabilities of being manipulated or fashioned by established methods, and in particular instances, specific properties of resistance to erosion, corrosion, wear, impact and fatigue. Perhaps this adaptability is best exemplified in the case of light alloys, whereby scientific alloying of aluminium or magnesium bases with other elements, combined with specific thermal treatments, have imparted increased strength, durability, and, under limited conditions, resistance to corrosion, to a whole range of alloys without any appreciable sacrifice of the great advantage in initial lightness of these two base metals. In view of this, these metals, which are conveniently designated “light alloys,” have become exceedingly popular, particularly since the majority of them are eminently suitable for fabrication in the form of diecastings, which permit the reproducibility of exact forms in large quantity production. The mechanical features of light alloys, together with their capacity to be machined, or otherwise finished to shape and dimensions, are fairly widely known, but their ability and relative merits to resist various conditions of corrosive influence are not so clearly elucidated. The readers of this journal arc naturally concerned primarily with finishes of protective value rather than with those of decorative importance. In general engineering considerable confusion exists as to the behaviour of aluminium and its alloys under deleterious influences, and this tends to retard their general adoption, even though their individual mechanical properties may make them highly desirable. In some cases most unnecessarily elaborate finishes are applied for ultra precautionary purposes, while in others a complete ban is exercised rather than incur any risk. In the aircraft industry, on the other hand, the demand for minimum weight consistent with requisite strength has provided the impetus for their adoption, which in turn has led to the development of appropriate finishing methods. Even in this sphere a comparative survey of finishing methods and their efficiency covering a range of popular alloys should prove to be of interest.

ALUMINIUM alloys have been important structural materials in aircraft from very early days, and there is no doubt that the course of aeronautical development would have been very different without them. It would be pointless to review the classification of these alloys and their respective fields of application in quite the same way as was done in the two previous articles of this series, those on titanium and magnesium. The aircraft industry has used many of the traditional alloys for years, and is highly familiar with their possibilities and limitations. In this article we shall outline, in the first place, the extent of present alloy development, giving some special attention to matters of particular aeronautical significance, and then limit further consideration to certain specific types of alloy which, for one reason or another, are the most promising as well as being the most difficult to use successfully in aircraft structures. These alloys are all of the high‐strength precipitation‐hardening type.

Aluminium alloys are being employed very widely as galvanic anodes for cathodic protection. Aluminium‐zinc‐mercury and aluminium‐zinc‐indium are the popular alloys that are used as anodes. In general, the alloying ingredients activate aluminium and maintain uniform dissolution. In the present investigation, the role of addition of gallium in the ternary alloy of aluminium‐zinc‐indium has been studied by making use of polarisation studies, capacity measurements and galvanic current measurements.

One of the most pressing problems of our times is the supply of adequate quantities of drinking water in areas not bestowed with abundant natural resources. Studies have shown the desalting of seawater to be economically sound for certain localities. Of all the available methods, the multi‐stage flash distillation is a proven method. The MSF type desalination plants may be operated independently (single purpose) or linked to power stations (dual purpose). In the MSF type desalination plants, the largest single item of cost is heat exchanger tubes. Design studies have shown that about one‐tenth of a square foot of condensing surface is required to produce one gallon of fresh water per day. For a combined capacity of one billion gallons per day at ¼ sq. ft. of tube, a tube length of 80,000 miles would be required. In MSF type desalination plants, the initial capital cost swallows up to 33% of the money, operating costs about 21% and the remaining 26% goes on power. The colossal amount of heat exchanger surface required in MSF type plants makes it mandatory to investigate new condenser tube materials which may provide ease of fabrication, maximise economy and be abundantly available.

In this article a resume is given of the principal obsevations made during the course of exposure in a natural atmosphere during some twenty years, while choosing the most characteristic examples. The following points will be examined: Resistance to spray and mist of aluminium‐magnesium, aluminium‐magnesium‐silicon, aluminium‐ zinc‐magnesium, and aluminium‐copper magnesium rolled alloys, and of cast alloys; Behaviour of welds, and of contacts with steel and cement; Behaviour during immersion in the sea, and corrosion by differential aeration; Protection by anodisation. These observations have been made during exposure at the experimental stations of the Pechiney Group, in marine atmospheres at Salin‐de‐Giraud (Mediterranean), Saint‐Jean‐de‐Luz, Biarritz and Ostend, and in an industrial atmosphere at Aubervilliers.

The purpose of this paper is to explore the use of fly ash and graphite particles as low cost reinforcing materials for improved wear resistance, enhanced mechanical properties and reduction in density of hybrid composites.

The AlSi10Mg/fly ash/graphite (Al/FA/Gr) hybrid composite was synthesised by stir casting method. The dry sliding wear and friction behaviour of hybrid composites were studied using pin-on-disc machine by varying parameters like load and weight fraction of fly ash, and compared with the base metal alloy and aluminium-graphite composite. The tests were conducted with a constant sliding speed of 2 m/s and sliding distance of 2,400 m.

The hybrid composites exhibit higher hardness, higher tensile strength and lower density when compared to unreinforced alloy and aluminium-graphite composite. The incorporation of fly ash and graphite particles as reinforcements caused a reduction in the wear rate and coefficient of friction (COF) of the hybrid composites. The improvement in the tribological characteristics occured due to the load carrying capacity of hard fly ash particles and the formation of a lubricating film of graphite between the sliding interfaces. The wear rates and COF of unreinforced aluminium alloy and composites increase with an increase in the applied normal load. The wear rates and COF of hybrid composites decrease with an increase in the fly ash content. 9 wt.% fly ash and 3 wt.% graphite reinforced hybrid composite exhibited the highest wear resistance and lowest COF at all applied loads. Abrasive wear and delamination were dominant in the mild wear regime of aluminium alloy and composites. Due to subsurface deformation and crack propagation, plate-like wear debris were generated during delamination wear. In the severe wear regime, the dominant wear mechanism was adhesive wear with formation of transfer layers.

It is expected that these findings will contribute towards the development of lightweight and low cost aluminium products with improved tribological and mechanical properties.

The wear and friction data have been made available in this article for the use of Al/FA/Gr hybrid composites in tribological applications.

The purpose of this study is to develop new Al‐based bearing alloys which have better properties than classic commercial bearing materials and to analyze tribologic properties of these alloys under dry sliding conditions experimentally.

Four different aluminium alloys were produced with casting method and tested on pin‐on‐disc wear testing machine. Friction coefficients and weight losses of the samples were determined under various working conditions in consequence of the experiments. Hardness, surface roughness, and surface temperatures of the samples were measured.

The results of the experiment show that friction coefficients vary by surface pressure and sliding speed. Al15Pb3.7Cu1.5Si1.1Fe and Al15Sn5Cu3Si alloys have lower friction coefficient values than other alloys. Al8.5Si3.5Cu alloy has the biggest wear resistance. Al15Pb3.7Cu1.5Si1.1Fe and Al15Sn5Cu3Si alloys are the most worn materials. Al8.5Si3.5Cu alloy has the lowest wear rate.

When the comparison was done between commercial Al alloys and developed Al alloys in this study, it was seen that Al15Sn5Cu3Si and Al15Pb3.7Cu1.5Si1.1Fe alloys have lower friction coefficient values than other commercial alloys.

The effects of the elements except aluminium composing alloys upon tribologic properties were analyzed. Some of the alloy elements were seen to improve tribologic properties whereas some downgrade. When the results are evaluated, Al15Sn5Cu3Si and Al8.5Si3.5Cu alloys containing Si and Sn can be preferred among the aluminium alloys that will work under dry sliding.

This paper reveals new bearing materials. These alloys can be used in journal bearings.

Seizure resistance of the cast graphite particle‐aluminium composite alloys, containing graphite particles of varying sizes has been studied using a Hohman wear tester. The size of the spheroidal graphite particles was varied from 30 µm to 400 µm, and in one case 80 µm size flake graphite was used to observe the effect of shape of graphite. When the graphite content of graphitic aluminium alloys is more than 2 per cent, these alloys can be self‐mated under condition of boundary lubrication without seizing. The size and shape of the graphite particles had no significant effect on the seizure resistance of these alloys, in the range of conditions investigated in this study. This is attributed to the extensive deformation and fragmentation of graphite due to the low yield strength of the aluminium matrix and the low flow stress of the graphite particles. During wear, the deforming aluminium matrix accentuates the deformation and fragmentation of subsurface graphite particles and causes them to come to the mating surface, thus providing continuous lubrication and preventing seizure. Even after a short run‐in period, a continuous layer of graphite is observed on the mating surfaces of graphite particle‐aluminium composite alloys. This layer persists even after extensive wear deformation.

The aluminium alloys are rapidly gaining a worldwide attention because of the economical and technical advantages they offer in applications encountering marine and similar other aggressive environments. A list of such alloys is given in Table 1. Several factors such as high weight to strength ratio high thermal conductivity, satisfactory resistance to corrosion and the economic feasibility of these alloys make them attractive candidates for the next decade as against the conventional copper and nickel alloys. The economic consideration assumes even a greater magnitude when the requirements and the purchasing potentials of the third world are seriously considered. The good features of these alloys are to some extent counteracted by the necessity for environmental modifications required to overcome the potential hazards of corrosion such as pitting, galvanic corrosion, erosion‐corrosion, crevice corrosion, and others. The variation of sea water chemistry effects the kinetics of the dissolution of aluminium alloys largely.