There are a wide variety of wrought aluminum alloys, each developed to provide specific properties. Getting the strength you need in an aluminum alloy requires knowledge of the effects of alloy composition, cold-working, and heat treating on aluminum metallurgy and properties. A good understanding of how aluminum alloys behave and what can be done to modify their properties is critical for being more productive and profitable. The course takes about one hour to complete and consists of one module and a final exam. Also, quizzes and problems give you opportunities to apply the concepts taught.
PROVISION is made, in the piston and rings described by the author, for an adequate flow of heat from all parts of the piston-head to the cylinder-wall by means of adequate cross-section of aluminum alloy in the head and a tongue-and-groove type of piston-ring structure which provides a greater amount of surface than is usual for heat transfer. A labyrinth oil-seal is provided which aids heat transference and prevents leakage past the piston-rings, and the heat transfer is said to be such that the heat does not destroy the oil seal between the piston and the ring. Charts are included that show the effects in reduced temperatures, oil consumption and gas leakage with the construction described. Attention is given also to a skirt construction most suitable to use with the piston-head and rings described.
ALUMINUM and magnesium, being the lightest commercial metals and therefore the most suitable for aircraft construction, are discussed in their pure and alloyed states. Physical properties of the pure metals and their alloys are given and the effects of adding small quantities of alloying elements are shown. Heat-treating as a means of increasing the strength per unit weight of the alloys is discussed at length, together with the effects of natural aging and artificial aging at elevated temperatures and of quenching in hot and in cold water after heat-treating. The several types of corrosion are considered and resistance to corrosion of the metals and their various alloys are discussed. Protection afforded to aluminum alloy by a surface coating of pure aluminum is described, and other methods are mentioned.
A NUMBER of the more important commercial alloys having aluminum as their base are discussed by the author, who points out their main physical characteristics and outlines methods which can be used in their fabrication, indicating in a general way which alloys are best suited to various aircraft-engine requirements. Tables are given showing chemical compositions and physical properties, including a table of physical properties of various casting alloys at elevated temperatures. Special-purpose alloys are commented upon, and also a new aluminum alloy for pistons which is beginning to find commercial application and possesses properties particularly desirable in aircraft engines. Recent developments in magnesium alloys and their application to aircraft-engine design are specified, tables of physical properties are given, and comments are made on the characteristics of the material as compared with aluminum alloys.
AT first believed immune, aluminum alloys have been found extremely susceptible to both surface corrosion and intercrystalline corrosion. The latter goes on under paint that has been applied to imperfectly cleaned surfaces, and shows only as blisters. Because of this, it has become commonplace to break with the fingers the ribs and the trailing edges of duralumin lower wings and tail-surfaces. Contact of duralumin with brass or steel hastens corrosion, and protective paint coverings are dissolved by dope where fabric surfaces meet metal parts. All-duralumin structures are not considered suitable for sea-going aircraft unless all joints and seams are of water-tight construction, not only in hulls but in other members of the structure. Corrosion over the land is much less severe. Few manufacturers seem awake to the importance of corrosion. The fight to avoid it should begin with avoiding seams that are difficult to protect and hollow members that cannot be sealed hermetically.
ACHIEVEMENTS of the last ten years in increasing the power-weight ratio of aircraft engines are stated and contributing factors are analyzed. Aluminum alloys have replaced cast iron and steel for certain parts, not entirely because of their lower weight but because of a combination of properties which better fit them for the task. Similar considerations must govern the replacement of aluminum-base alloys by those of magnesium. The most promising immediate field for the magnesium alloys is said to lie in applications wherein strength and lightness are the main considerations and high-temperature properties are of secondary importance. Properties of magnesium castings and forgings are compared with those of castings and forgings of the aluminum alloys. Features of design are discussed which should receive special attention when changing a part from aluminum to magnesium. Machining practices for magnesium are covered in some detail.
COMPARATIVELY large rake and clear angles required for best results leave a relatively thin cutting-edge on a cutting tool for aluminum. One difficulty encountered is that tools of such form are not always available or suitable, for various reasons, for instance, small tools of various types are available only with cutting edges suitable for steel and bronze, and the desirable amount of top rake cannot well be provided on circular form-tools. Tool bits of various sorts can be reground to the desired angle. A simple round form of tip that is shown can be utilized in tools for various purposes, including use as inserted teeth in a face-milling cutter. High-speed-steel tools are suitable for most aluminum alloys, but alloys containing a high percentage of silicon can be machined to advantage only by using cemented tungsten-carbide. Machine-tools should be suitable for high speed.
COMPROMISES are necessary in designing a piston, sacrificing the quality of least importance under the given conditions. Aluminum alloy is seen as a most desirable material because of its high conductivity and low rate of absorbing heat from hot gases. Aluminum-alloy pistons are now made for oil engines with bores up to 18 in., as well as for small gasoline engines, those described in this paper having their expansion controlled by steel bands embedded in the aluminum but not bonded thereto. Slots cast in the piston allow for linear expansion of the alloy without a corresponding increase in piston diameter and change in cylinder clearance. Advantages of strut-type pistons are shown by thermal diagrams. Illustrations show large pistons and engines in which they are used. Cores and steel inserts for producing such pistons are shown also.
Several years ago some of the most prominent leaders in automotive industries cooperated to form a purely engineering group that had as its primary purpose developing a type of rigid-airship construction in which the public would have confidence. It was conceived that such an airship should be (1) Fireproof (2) Weatherproof (3) Durable and permanent in structure (4) Navigable in practically all kinds of weather (5) Economical in the use of buoyant gas and ballast To meet all of these requirements it was decided, after mature consideration, that a substantially all-metal construction was imperative.
Iron ranks first of all the metals; copper, lead and zinc come fairly close together in tonnage; tin ranks next; and aluminum is fifth of the non-ferrous metals. The place of aluminum in the automotive industry is shown in a diagram and another brings out the production of copper and aluminum, both receiving comment. The metallography of aluminum alloys is discussed in some detail, as well as the phenomena of growth and aging, charts and photomicrographs being shown and commented upon. The effect of alloying on physical properties is treated in a similar manner in considerable detail and a comparison of aluminum with other metals follows. Forging alloys are described and some miscellaneous aluminum-alloy forged parts are pictured. The advantages of forging alloys are enumerated and many of their present uses specified; other contemplated uses for the newest alloy are for cast disc-wheels for passenger cars, differential carriers and cast rear-axle housings.
Although aluminum is the most abundant metal in the earth's crust, it was not until the early eighties that means were discovered for reducing it from its ores in such quantities and at such cost as to make it a commercial possibility. The world immediately began to find uses for this material. Two groups developed; one, assuming for aluminum properties that it did not possess, thought that it would in time replace all other metals; the other, which, reacting from the first-mentioned view due to failures and disappointments, thought it had little use. It was afterward realized that much research was necessary to make aluminum a really commercial metal. One of the main aims of the automobile engineer is to obtain lightness combined with proper strength. The paper deals with decreasing the weight of automobiles by more extended use of aluminum alloys. The physical properties of aluminum are described in considerable detail and its varied uses are enumerated.
THIS paper includes the results of a study to determine how best to fabricate aircraft components made from precipitation-hardening aluminum alloys so as to take full advantage of the superior mechanical properties of these materials, and yet have parts that can be fabricated readily with a minimum of shop difficulties. The following characteristics of these alloys and problems incidental to their use are studied: mechanical properties, heat-treating operations, effects of cold work, problems connected with various forming operations, methods of attachment, machinability, finish requirements, means of inspection and identification of the various materials and their several tempers, and shop assembly procedures. The following shop fabrication procedures are recommended: 1. In cases where design dictates the use of precipitation-hardening aluminum alloys, the detail parts should be formed, whenever practicable, in the as-quenched solution heat-treated condition. 2.
THE present shortage of sheet steel has made the substitution of aluminum worth while for some automotive parts, the authors report, despite the higher cost of aluminum per pound. Two aluminum alloys are suggested for automotive applications. Alcoa No. 2 automotive sheet is said to furnish a good combination of properties from the standpoint of strength, resistance to corrosion, workability, and price. Alcoa No. 3 is said to be superior to No. 2 in workability and to have excellent resistance to corrosion, although its strength is somewhat lower than that of No. 2.
TODAY’S airplane has much of its structure subjected to temperatures above the range where aluminum alloys are advantageous. Titanium appeared to have considerable weight advantage over stainless steels in this moderate temperature range. A preliminary screening program of its fabrication characteristics established its basic relationship to other materials, such as aluminum alloys, magnesium, and stainless steel, with which we were familiar. From this, design and tooling practices, as well as processing and manufacturing techniques and procedures, were established, according to the author. The approach is one of determining the characteristics of the material and adapting designing and manufacturing practices compatible with the material. This paper received the 1951 Wright Brothers Medal.
THE bonded bimetallic brake drum has been developed to help solve the increasingly difficult problem of providing satisfactory braking service for modern cars. These drums have an aluminum-alloy housing bonded to a cast-iron liner. In this combination, the cast iron provides the wearing surface and the aluminum alloy provides the high heat conductivity and low weight. The result is an improvement in the rate at which heat is dissipated and a lower unsprung weight for the car. These brake drums have also been found to help considerably in eliminating squeal. In England, it is reported, several car manufacturers are already using these drums successfully.
INASMUCH as new developments in the field of aluminum alloys are immediately reflected in the aircraft industry, the author of this paper reviews past and present achievements which relate directly to aviation needs of the future. The alloys in use today are described as satisfactory. They have been brought to this point by intensive research leading to high strength, resistance to corrosion and fatigue, and ease of fabrication. A clearer understanding of the problems associated with present alloys is responsible for the presentation of successful new alloys. The author describes how a recent newcomer, 75S, has already attained dominance in the extrusion field, and has made measurable inroads in the sheet, plate, and forging fields. He also describes how military demands for alloys of higher and higher strengths have led to a complete revision of concepts concerning elongation, followed by a reappraisal of the need for artificial aging.