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CHAPTER – 3
3.1 EXPERIMENTAL WORK 3.1.1 Parent Metal
The parent metals employed in this study are AA7075 and SS304L of 25.4mm diameters and 150 mm length. The composition and mechanical properties of the starting parent metals given below :
Table 3.1 Chemical Composition
7075 Al Alloy
Table 3.1 Mechanical and physical properties
3.1.2 Specification of Friction Welding Machine
1.Spindle speed 1500 - 3000 RPM.
2.Spindle motor 11Kw/440V.
3.Component clamping 3 jaw worm drive chuck.
4.Total stroke 350mm.
5.Rapid Transverse 2000mm/min.
6.Spindle torque 20 Kgm.
7.Welding material capacity 60mm (max).
8.Maximum thrust 8000 Kgf.
9.While friction 2000 Kgf.
10. While welding (pressurizing) 8000 Kgf
Fig 3.1 Friction Welding Machine
3.1.3 Some Friction Welding Joints
Fig 3.2 Bi-metalic Specimen
Fig 3.3 Bi metalic Volve
Fig 3.4 CU-SS Joints for Plasma Research Institute
Fig 3.5 CU-AL Connector
Fig3.6 X-Ray Tube Rotor
3.1.4 Friction Welding Process
Friction welding is a solid state joining process that uses rotational motion and high axial pressures to convert rotational energy into frictional heat at a circular interface. The heat produced by this rubbing action raises the intersurface temperature of the two parts to the plastic state where the high thrust load extrudes metal from the weld region to form an upset. When sufficient energy input has occurred, the rotation is stopped and thrust load is increased, to forge the parts together and form a solid state bond. The flash may be removed as part of the machine cycle
3.1.5 Principle of Friction Welding
Table 3.3 Friction Welding Parameters
Heating Time (s)
Upset Time (s)
Fig3.7 Friction Welding Operation step I
In the ficion welding, the specimen AA7075 and SS304L material were prepared. The two metallic part to be jointed are securely chucked, one in a tail stock fixure and the other in the rotating spindle.
Fig 3.8 Friction Welding Operation step II
The spindle begins to rotate and the parts are pressed in contact with each other with a considerable friction force. Friction duration is controlled by time. The purpose of the first friction phase is to be burn off any light oils or light oxides at the weld interface.
Fig3.9 Friction Welding Operation step III
The final phase in friction welding is the forge phase. The spindle is forced to a stop and both components are pressed against each other at extreme pressure and allowed to cool. The fore phase controlled by time.
Fig3.10 Friction Welding Operation step IV
The is no control as to how much material is displaced in the forge phase but it is dependent on the amount of heat generated in the second phase and the amount of pressure applied. Force phase duration is controlled by time. Soften material begins to extrude in response to the applied pressure, creating an annular upset. Heat is conducted away from the interfacial area for forging to take place.
Fig3.11 Friction Welding Operation step V
Table3.4 Observed Physical Data On The Friction Welded Sample
Initial Length L1 (mm)
Initial Length L2 (mm)
Finial Length after Welding
3.1.6 Friction welding:
in friction welding, the specimen aa7075 and ss304l material were prepared. the two metallic parts to be jointed are securely chucked, one in a tailstock fixture and the other in the rotating spindle. the spindle rotating is bought to a predetermined r.p.m to produce the desired surface velocity and to generate the proper level of kinetic energy in the rotating inertial mass. the flywheel may or may not be attached, depending on the kinetic energy requirements of specific applications. at the desired rpm the spindle drive is disengaged allowing only the kinetic energy to drive the spindle. when the drive has disengaged, the controlled hydraulic ram pressure forces the parts together at the faying surfaces. the hydraulic ram may be mounted either at the headstock or tailstock depending on the design of the machine. friction between the two surfaces converts the kinetic energy to heat which combines with the thrust force to create a forging action and welds the two parts together thereby stopping the spindle.
Fig3.12 Welding specimen AA7075and SS304L
Fig3.13 Welding specimen AA7075 and SS304L
Fig3.14 Welding specimen
Fig3.15 Welding specimen
3.2 TENSTILE TEST
3.2.1 The Preparation Of Test Specimens
Plates and shapes are almost always used in as-rolled conditions; the tests applied to them are usually fewer and less complicated than tests applied to bars, in which properties are frequently enhanced by heat treatment. Tension and bend tests are commonly specified by the trade to determine the suitability of plates for the intended purpose. The conventional tension test specimen is cut approximately 18 in long by 2 in wide and is machined over the gauge length to the width of 1.5 in. With this specimen, percentage elongation is measured in 8 in.
When a machined test specimen is necessary it is permissible to machine a specimen to the form and dimensions of the standard tension specimen 0.5 inch in diameter or to the smaller size proportional to the specimen. Examples of specimens of smaller size are shown in fig
G-gage lemgth D- diameter of rod
A-Length of reduced section R- radius of fillet
The gage length for the measurement of elongation is often 2in regardless of the size of the specimen, but to minimize the effects of specimen size on result of elongation, the gage length should be 4 times the diameter or distance across flats of the test section (in octagonal, hexagonal or square cross sections. For rods, bars and shapes as large as 1.5in in diameter or thickness the axis of the test specimen should coincide with the axis of the piece. For larger sections, the axis of the specimen should be located midway between the centers and surface of the piece. In testing bars and shapes less than 0.5 in thick, a specimen is frequently used that has the dimensions of the standard tension test specimen for sheet, with a reduced section 0.5in wide and 2.25in in long. For testing plate thinner than 0.5in, a specimen of this type is used. For plate 0.5in thick or more, the standard tension specimen 0.5in in diameter is used. When plate no more than 1.5in thick is to be tested , the axis of the specimen should be midway between the two surfaces of the plate, but for thicker plate the axis should be midway between centre and surface.
Tension tests are usually made to determine yield strength, tensile strength and elongation. The yield strength for most nonferrous materials is specified as the stress corresponding to an offset of 0.002in per inch. The yield strength readily determined by a testing machine that is equipped with an autographic extensometer, which draws a load-strain curve as the test is being made. Yield strength is sometimes specified and determined as the stress corresponding to a definite amount of extension under load; It is case the yield strength is determined either with an autographic extensiometer or merely an indicating extensiometer. It is recommended that all tension tests be made in accordance with ASTM standard methods of tension testing of metallic materials.
3.2.2 Testing Procedure
The specimen to be tested is fastened to the two end jaws of the UTM. Now the load is applied gradually on the specimen by means of the movable cross head, till the specimen fractures. During the test, the magnitude of the load is measured by the load measuring unit. A strain gauge or extensometer is used measure the elongation of the specimen between the gauge marks when the load is applied
Fig3.16 Tensile test: Model: UTE 60M/c, SI.No: 6/2007-3672
Table3.5 Tensile Test result
3.3 Hardness Test :
Hardness may be defined as the ability of a material to resist scratching, abrasion, cutting or penetration.
The hardness test is performed on the material to know its resistance against indentation and abrasion.
3.3.1 Types of Hardness Tests:
The three most commonly used hardness tests are
Brinell hardness test
Vickers hardness test
Rockwell hardness test
3.3.2 Basic Common Principle:
The hardness is measured from an intendation produced in the component by applying a constant load on a specific intender in contact with surface of the component for a fixed time. A large impression for a given load indicates that the material is soft material, and smaller impression indicates a hard material.
3.3.3 Rockwell Hardness Test:
The Rockwell hardness test is probably the most widely used methods of hardness testing. The principle of the Rockwell test differs from that of the others in that the depth of the impression is related to the hardness rather than the diameter or diagonal of the impression.
Rockwell test are widely used in industries due to its accuracy, simplicity and rapidity. In the test, the dial gives the direct reading of hardness, no need for measuring intendation diameter or diagonal length using the microscope.
3.3.4 Rockwell Scales:
There are many Rockwell scales. But the most commonly used are
B-scale (1/16 inch diameter steel ball intender; 100kg load) used to measure the hardness (HRB) of non-ferrous metals.
C-scale (120° diamond cone intender, called a BRALE; 150kg load), used to measure the hardness (HRC) of steels
3.3.5 Rockwell hardness test:
A Rockwell test is made by slowly elevating specimens against the intender until a minor load has been applied as indicated by an index hand on a dial gage. A major load is applied by realising a loaded lever system; the speed of descend of the lever is controlled by an adjustable oil dashpot. The completion of the descent of the lever, the major load is removed and, with the minor load still acting. The Rockwell hardness number is read on the dial gage. This number is based on the depth of indentation less than the elastic recovery following removal of the major load, less penetration resulting from the minor load because of the reversal of the order of the number on the dial gage, a high number is associated with the shallow impression made in hard material, and a low number with deep impression in soft material. Several different Rockwell scales, each associated with a particular combination of load and intender are necessary to cover the range of hardness encountered in materials.
The original and most commonly used Rockwell scales are B and C both obtained with normal tester. To obtain the best possible performance from a Rockwell tester the following procedure is recommended.
The tester should be placed so that vibration does not seriously affect the readings of the dial gage.
For the minor load to be properly applied, the large needle on the dial gage should be at ˝set˝ within plus or minus five scale divisions. If the elevating operation results in the needle stopping within this range, but not on ˝set˝ no further adjustment should be made by means of the elevation screw but the dial should be rotated to bring set under the needle.
On the normal tester the dashpot which control the speed of application of the major role should be adjust so that the operating crank completes its travel in 5 seconds with no specimen on the machine but with the machine setup to apply a major load of 100Kg. in the similar manner the superficial tester is set for 7 sec with major load of 30Kg.
The machine should apply the major load that is the operator should avoid any manual pressure on the crank. After realizing the lever system. The major load is allowed to act until either the pointer on the dial gage suddenly slows down or the weight arm is completely free from control of the dashpot. The latter is preferred because it is a clear cut end point.
The performance of the machine should be checked frequent against the standard test blogs supplied by the manufacturer. If the hardness values obtained differs from that inscribed on the test blog, the machine should be adjusted according to the instructions supplied by the manufacturer.
Because the accuracy of hardness determination depends on an accurate measurement of the depth of penetration, particular care should taken to seat the intender and anvil firm ly. Any vertical movement at these points result in additional depth being registered on the gage and therefore means a false number.
Fig3.17 Hardness test: Model: RAB M/c, SI.No: 08/07/009.
Fig3.18 Hardness test: Model: RAB M/c, SI.No: 08/07/009.
Table 3.6 Hardness Test result
3.4 Impact Test
Impact test is performed to study the behavior of materials under dynamic load i.e. suddenly applied load.
3.4.1 Impact Strength Defined:
The capacity of a metal to withstand blows without fracture is known as impact strength or impact resistance.
The impact test indicates the toughness of the material i.e. the amount of energy absorbed by the material during plastic deformation. The impact test also indicates the notch sensitivity of a material. The notch sensitivity refers to the tendency of some normal ductile materials to behave like brittle materials in the presence of notches.
In an impact test, notch is cut in the standard test piece which is struck by a single blow in a impact testing machine. Then the energy absorbed in breaking the specimen can be measured from the scale provided on the impact testing machine.
uses a test specimen of size 55mm x 10mm x 10mm. The V-notch angle is 45° and the depth of the notch is 2mm. The Charpy specimen is placed in the vice as a simply supported beam.
Fig 3.19 The Charpy notch-impact test specimen
3.4.2 Testing Procedure:
The general procedure to conduct an impact test is given below
The AA6082 specimen is placed in the vice of the anvil.
The pendulum hammer is raised to known standard height depending on the type of specimen the tested
When the pendulum is released, its potential energy is converted into kinetic energy just before it strikes the specimen.
Now the pendulum strikes the specimen. It may be noted that the Izod specimen is hit above the V-notch and the Chary specimen will be hit behind the V-notch.
The pendulum, after rupturing the specimen, rises to the other side of the machine.
The energy absorbed by the specimen during breaking is the weight of the pendulum times the difference in two heights of pendulum on either side of the machine.
Now the energy i.e. the notched impact strength, in foot-pounds or meter-kg, is measured from the scale of the impact testing machine
Fig3.20 Impact test (Charpy at room temperature (30°C)): V Notch: 2mm at weld center,
Table 3.7 Impact Test result
3.5 Preparation for Microscopic Examination:
For microscopic examination , it is usually necessary to cut specimens of a convenient size of polishing. These can be obtained by sawing or shearing but care should be taken to avoid overheating the specimen or alerting the structure in any manner. The next step in the preparation of a metallographic specimen is the removal of all oil, grease, drit and other foreign material. Specimen too small to be handled conventionally during polishing should be mounted in some manner. The mounting of specimens can be accomplished in several ways. For instance, with samples of sheet, a pack can be made by binding a number of pieces of sheet together by means of machine screws. In the making of a composite specimen of sheet or foil, the piece is assembled in the pack or sometimes separated by filler pieces of an aluminium alloy. Other metals should not be used as filler pieces in composite specimens; the pack should be clamped tightly to minimize capillary retention and subsequent exudation of solutions from crevices.
The general practice is to embed any small or irregular-shaped specimen in a mounting medium. The most economical and convenient method consists in placing the specimen in a ring of aluminium cubing and filling the ring with melted sulphur. Sulphur does not chip during polishing and is unaffected by the etching reagents commonly used. Other mounting materials, such as sealing wax or dental cement may be employed. If a press for mounting specimens is available, Bakelite are one of the transparent or semi transparent plastics can be used. It is important to avoid any mounting material that will cause galvanic attack during etching or that is severely attacked during the etching procedure.
The following procedure is recommended for the preparation of specimens for microscopic examinations.
Draw the specimen over a long-angle lathe file to obtain a plane surface and to remove any distorted metal from sawing operation.
Rub specimen on 180-grain aloxite paper to remove file marks, and then successively on No. 0 and 000 metallographic emery papers that have been coated with a solution of paraffin and kerosene. This coating helps keep the specimen bright and prevents particles of abrasive from becoming embedded in the surface. Solution is made by dissolving 50 gram of paraffin in 1litre of kerosene. The specimen should be turned about 90degree to the direction of polishing, at each step in the process.
Polishing on a rotating disk covering with kittens ear broadcloth or gamal cloth using a water suspension of 600 alundum flour or a similar material as the abrasive. A quantity of the abrasive is placed in a flask with water and is shaken until it is in suspension. In this way, the mixture can be conventionally supplied to the pad while the specimen is being polished. The polishing disk should be operated at about 250 to 300 rpm and the specimen should be held on the pad about 2 to 3 inch from the centre of the disk. The pad should finally be washed free of the coarser particles of the abrasive by means of a stream of water form a wash bottle, and the polishing with this abrasive should be completed by using a suspension from which all the coarse particles have setelled.
Polish finally on a rotating disc covered with kittens ear broadcloth or gamal cloth and operated at a speed of 150 to 200 rpm, using heavy magnesium oxide powder as a polishing medium. The pad should be kept moist with distilled water and a small quantity of magnesium powder should be worked in to it with the palm of the hand. Any gritty particles or excess powder should be brushed off. During polishing the pad should be kept moist by adding distilled water from a water bottle as needed. The pressure and time required for polishing a specimen are influenced by both the composition and the temper of the specimen.
When a satisfactory polish has been secured, the specimen should be washed in the stream of warm tap water and dried by blowing the excess water from the surface. The polished surface should not beer th touched or rubbed against anything, otherwise the finish may be marred. Specimens will retain their finish indefinitely, provided they are kept with the place where dust and dirt from the atmosphere will not collect on the specimen.
3.5.1Constitutions in Aluminium Alloy:
In the metallographic examinations of aluminium alloys, it is frequently necessary to identify the constituents that appear in the microstructure. In general the constituent in aluminium alloy consists of elements such as silicon that do not combine with aluminium to form compounds and therefore are present in the elemental state. Intermetallic compounds formed by the combination of one or more alloying elements with aluminium (Cu, Al2 and FeAl3). Intermetallic compounds that are formed by combinations of 2 or more elements other than aluminium and that are stable in aluminium.
3.5.2 Identification of Constituents :
The first attempt to identify constituents should be made on the unetched specimen, using color and manner of occurrence as a means of differentiation. Some of the more comm. identified on constituents such as CuAl3, Si, Mg2Si and β Al-Mg can be readily identified by the polishing characteristics, color and manner of occurrence. Others, more difficult to identify, are sometimes present and necessitate the use of various etching reagents.
For judging the color of constituents, it is advisable to employ light approximately the color of daylight. Addition of a wratten 78A filter, which has a bluish tint, converts the light of a Eastman neutral tint filter to approximately to that of daylight. Any white light will give about the same result, although the use of 78A filter will help in the separation of different constituents. Examination for identification is usually made at a magnification of 500 diam with a lens combination comprising a 4mm objective and a 10× ocular.
3.5.3 Microstructure of aluminium alloy
Commercial aluminium alloys are generally of a hypoeutectic type and solidification begins with a separation of aluminium or aluminium-rich solid solution as primary dendrites. During solidification of these dendrites , the alloying constituents tends to concentrate in the remaining liquid phase producing a structural condition known as coring and a discontinuities or continuous network of constituents at intersection of dendrites and along the grain boundaries. Further changes in structure results from different rates of cooling after solidification, and from various thermal and mechanical treatments. The constituents in aluminium alloy are found at the interstices of the dendrites and along grain boundaries in the as-cast condition, and are generally distributed throughout the matrix in material in the wrought condition. The microstructure of castings is governed largely by chemical composition, rate of solidification and thermal treatment. The microstructure wrought product is influenced, also by type and amount of working, as well as by various thermal treatments that the products receive.
When an aluminum alloy of heat treatable type is subjected to solution heat treatment, marked changes occur in the microstructure. The most important change result from solution of various hardening constituents during heating cycle.
Fig 3.21 Microstructure for AA7075(parent metal)
The parent metal aluminum alloy 7075 stature shows that the distributions reinforcement in the respective matrix are fairly uniform. Reveals the homogeneity of the composite. The fine dispersion of second phase precipitates was evident both in the grains and along the grains with solution annealed.
Fig3.22 Microstructure of SS304L (parent metal)
The parent metals stainless steel304L austenitic stainless steel contains equiaxed grains with occasional twinning. The parent metal of stainless steel grain size coarses size in this metal
Fig3.23 Microstructure study of AA7075 and SS304L
Stainless steel 304L have lower thermal conductivity and greater hardness at high temperatures compared to Aluminium alloy 7075. For this reason SS304L does not undergoes extensive deformation. The coarser grain structure observed in low forge pressure combination can be attributed to lower degree of working of the material than at high forge pressure that result in a higher degree of working. The central region consists of fine grains,while the pheripheral region consists of coarse grains, The fine grain size at the central region is due to dynamic recrystallization. The temperature of the peripheral region woul be higher and therefore exhibits the coarse grain size. Despite the coarse grain structure at the periphery, the overall bond region remains stronger than the parent material.
25formed by the combination of one or more alloying elements with aluminium (Cu, Al2 and FeAl3). Intermetallic compounds that are formed by combinations of 2 or more elements other than aluminium and that are stable in aluminium.
Stainless steel 304L have lower thermal conductivity and greater hardness at high t