Description:FIELD OF THE INVENTION
[0001] The present disclosure relates generally to the field of alloys. Particularly, the present disclosure relates to a lead and tin free Aluminum-Bismuth (Al-Bi) based alloy that exhibits improved machinability while maintaining the strength and other desired properties of the alloy.

BACKGROUND OF THE INVENTION
[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[0003] A machining process is limited by some natural features, one of these being the chip size and form, which is sometimes a serious obstacle to further advance in automated manufacturing. Moreover, a lack of chip control often leads to coarse surface finish and integrity, poor machining accuracy, high cutting forces and energy, and problems with chip removal from the machining zone.
[0004] Free machining aluminium alloys are well known and used in the industry. These alloys include free machining ingredients that are insoluble, but are soft and nonabrasive, and hence, help assist in chip breakage and tool life. It is a well-known fact that chip breaking is enhanced/promoted by the addition of Pb and tin to conventional aluminium alloys. Pb has poor solubility in solid aluminium and forms a soft, low melting point phase. However, across the globe, several directions and regulations are issued by the regulatory agencies of different countries that pose a restriction regarding the lead and tin content (particularly, the lead content) in aluminium alloys. This causes a big challenge for the global precision machining industry to find a new alternative free-machining, lead-tin-free alloys that may provide at least the same results in terms of productivity and efficiency.
[0005] Therefore, it would be desirable to develop a new and improved alloy or alloy composition that may overcome one or more limitations associated with conventional Al-based alloys. The present invention satisfies the existing needs, as well as others, and generally overcomes the deficiencies found in the prior art.
OBJECTS
[0006] Primary object of the present disclosure is to provide a lead and tin free Aluminium-Bismuth (Al-Bi) based alloy that may overcome one or more limitations associated with conventional Al based alloys.
[0007] It is an object of the present disclosure to provide a lead and tin free Al-Bi based alloy that exhibits improved machinability.
[0008] It is an object of the present disclosure to provide an Al-Bi based alloy that exhibits improved machinability while maintaining the strength (such as young strength, tensile strength, etc.) and other desired properties.
[0009] It is an object of the present disclosure to provide an Al-Bi based alloy that exhibits functional reciprocity.
[00010] It is an object of the present disclosure to provide an Al-Bi based alloy that is economical and easy to prepare.
[00011] Another object of the present disclosure is to provide a method of preparation of an Al-Bi based alloy with improved properties.

SUMMARY
[00012] The present disclosure relates generally to the field of alloys. Particularly, the present disclosure relates to a lead and tin free Aluminum-Bismuth (Al-Bi) based alloy that exhibits improved machinability while maintaining the strength and other desired properties of the alloy.
[00013] An aspect of the present disclosure relates to a lead and tin free alloy composition, said composition including: 0.1 to 0.2 wt% of Fe, 0.70 to 1.0 wt% of Si, 0.55 to 0.85 wt% of Mg, 0.6 to 0.90 wt% of Mn, 0.05 to 0.20 wt% of Cu, 0.01 to 0.03 wt% of Ti, 1.55 to 1.95 wt% of Bi, and the rest being Al. In an embodiment, the composition includes: 0.1 to 0.2 wt% of Fe, 0.70 to 1.0 wt% of Si, 0.55 to 0.85 wt% of Mg, 0.6 to 0.90 wt% of Mn, 0.05 to 0.20 wt% of Cu, 0.01 to 0.03 wt% of Ti, 1.60 to 1.90 wt% of Bi, and the rest being Al.
[00014] Another aspect of the present disclosure relates to a lead and tin free alloy including: 0.1 to 0.2 wt% of Fe, 0.70 to 1.0 wt% of Si, 0.55 to 0.85 wt% of Mg, 0.6 to 0.90 wt% of Mn, 0.05 to 0.20 wt% of Cu, 0.01 to 0.03 wt% of Ti, 1.55 to 1.95 wt% of Bi, and the rest being Al. In an embodiment, the alloy includes: 0.1 to 0.2 wt% of Fe, 0.70 to 1.0 wt% of Si, 0.55 to 0.85 wt% of Mg, 0.6 to 0.90 wt% of Mn, 0.05 to 0.20 wt% of Cu, 0.01 to 0.03 wt% of Ti, 1.60 to 1.90 wt% of Bi, and the rest being Al. In an embodiment, the alloy exhibits surface roughness after machining in the range of 0.4 to 0.6 µm Ra.
[00015] Further aspect of the present disclosure relates to process of preparation of an alloy.
[00016] Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the exemplary embodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION
[00017] The embodiments herein and the various features and advantageous details thereof are explained more comprehensively with reference to the non-limiting embodiments that are detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of the ways in which the embodiments herein may be practiced and to further enable those of skills in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
[00018] Unless otherwise specified, all terms used in disclosing the invention, including technical and scientific terms, have the meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. By means of further guidance, term definitions may be included to better appreciate the teaching of the present invention.
[00019] As used in the description herein, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
[00020] As used herein, the terms “comprise”, “comprises”, “comprising”, “include”, “includes”, and “including” are meant to be non-limiting, i.e., other steps and other ingredients which do not affect the end of result can be added. The above terms encompass the terms “consisting of” and “consisting essentially of”.
[00021] The terms “weight percent”, “percent by weight”, “% by weight”, and variations thereof, as used herein, refer to the concentration of a substance as the weight of that substance divided by the total weight of the composition and multiplied by 100. It is understood that, as used here, “percent”, “%”, and the like are intended to be synonymous with “weight percent”, “wt%”, etc.
[00022] In some embodiments, the numbers expressing quantities of ingredients, properties such as concentration, reaction conditions, and so forth, used to describe and claim certain embodiments of the invention are to be understood as being modified in some instances by the term “about”. Accordingly, in some embodiments, the numerical parameters set forth in the written description are approximations that can vary depending on the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable.
[00023] The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein.
[00024] The headings and abstract of the invention provided herein are for convenience only and do not interpret the scope or meaning of the embodiments.
[00025] The following discussion provides many example embodiments of the inventive subject matter. Although each embodiment represents a single combination of inventive elements, the inventive subject matter is considered to include all possible combinations of the disclosed elements. Thus, if one embodiment comprises elements A, B, and C, and a second embodiment comprises elements B and D, then the inventive subject matter is also considered to include other remaining combinations of A, B, C, or D, even if not explicitly disclosed.
[00026] The present disclosure relates generally to the field of alloys. Particularly, the present disclosure relates to a lead and tin free Aluminum-Bismuth (Al-Bi) based alloy that exhibits improved machinability while maintaining the strength and other desired properties of the alloy.
[00027] The present disclosure is on the premise that when Bi and Al are included as part of the alloy in the weight percentages as defined herein; they exhibit exceptional functional reciprocity and affords dramatic improvement in machinability of the alloy while maintaining the strength (such as young strength, tensile strength, etc.) and other desired properties of the alloy. Without wishing to be bound by the theory, it is believed that the improvement is owing to proportionate usage of ingredients viz. Bi and Al present in the alloy. The observed effect is unexpected and surprising.
[00028] An aspect of the present disclosure relates to a lead and tin free alloy composition, said composition including: 0.1 to 0.2 wt% of Fe, 0.70 to 1.0 wt% of Si, 0.55 to 0.85 wt% of Mg, 0.6 to 0.90 wt% of Mn, 0.05 to 0.20 wt% of Cu, 0.01 to 0.03 wt% of Ti, 1.55 to 1.95 wt% of Bi, and the rest being Al.
[00029] In an embodiment, the composition includes: 0.1 to 0.2 wt% of Fe, 0.70 to 1.0 wt% of Si, 0.55 to 0.85 wt% of Mg, 0.6 to 0.90 wt% of Mn, 0.05 to 0.20 wt% of Cu, 0.01 to 0.03 wt% of Ti, 1.60 to 1.90 wt% of Bi, and the rest being Al.
[00030] In an embodiment, the alloy composition includes 0.001 to 0.003 wt% of Cr and 0.01 to 0.04 wt% of Zn as impurity.
[00031] Another aspect of the present disclosure relates to a lead and tin free alloy including: 0.1 to 0.2 wt% of Fe, 0.70 to 1.0 wt% of Si, 0.55 to 0.85 wt% of Mg, 0.6 to 0.90 wt% of Mn, 0.05 to 0.20 wt% of Cu, 0.01 to 0.03 wt% of Ti, 1.55 to 1.95 wt% of Bi, and the rest being Al.
[00032] In an embodiment, the alloy includes: 0.1 to 0.2 wt% of Fe, 0.70 to 1.0 wt% of Si, 0.55 to 0.85 wt% of Mg, 0.6 to 0.90 wt% of Mn, 0.05 to 0.20 wt% of Cu, 0.01 to 0.03 wt% of Ti, 1.60 to 1.90 wt% of Bi, and the rest being Al.
[00033] In an embodiment, the alloy includes 0.001 to 0.003 wt% of Cr and 0.01 to 0.04 wt% of Zn as an impurity.
[00034] In an embodiment, the alloy exhibits surface roughness after machining in the range of 0.4 to 0.6 µm Ra.
[00035] In an embodiment, the alloy allows formation of discontinuous type Chip having size in the range of 10 mm to 50 mm.
[00036] The alloy of the present disclosure exhibits exceptional functional reciprocity and affords dramatic improvement in the machinability of the alloy while maintaining the strength (such as young strength, tensile strength, etc.) and other desired properties of the alloy. Further, the alloy of the present disclosure is economical as compared to the other commercially available alloys and exhibits better properties. It is believed that the improvement is owing to proportionate usage of ingredients viz. Bi and Al in the alloy, provides the improved machining either due to void formation due to the non-uniform deformation of bismuth and the aluminum matrix during the machining process or an effect related to bismuth being a low melting point constituent as compared to the base aluminum, allowing the formation of low melting phases like Mg3Bi2 (melting point of 260 °C) and Bi (melting point of 271 °C) that melts during machining and forms discontinuous chips, and a combination thereof.
[00037] The Alloy of the present disclosure can be prepared by any conventional method known to or appreciated by a person skilled in the art working in the pertinent field. Briefly, in a melt of Aluminium, master alloys viz. AlFe5%, AlSi10%, AlMn10%, AlMg10%, AlCu80%, Al-Ti10%, and Al-5%Bi are added in stoichiometric amounts and heated at around 660 °C to 750 °C to obtain a final melt composition. The final melt may be degassed with an inert gas such as Argon gas to remove any air bubble present therein before being cast into any product of desired shape or size such as 4” diameter cylindrical billets. Finally, products such as billets are extruded by using any conventional extrusion technique to obtain the extruded alloy.
[00038] The alloy of the present disclosure finds application in the preparation of products related to, included but not limited to, electrical, electronic and automotive parts, such as camera, clock, mobile phones, ABS manifolds, brake parts, hydraulic manifolds and valve blocks, A/C components, transmission valves and sleeves, steering yokes, drive shafts, electrical connectors, screws, gears, and the likes.
[00039] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the scope of the embodiments as described herein.
EXAMPLE
[00040] The disclosure will now be illustrated with working example, which is intended to illustrate the working of disclosure and not intended to take restrictively to imply any limitations on the scope of the present disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this disclosure belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice of the disclosed methods and compositions, the exemplary methods, devices and materials are described herein. It is to be understood that this disclosure is not limited to particular methods, and experimental conditions described, as such methods and conditions may vary.
[00041] AN ALLOY COMPOSITION

Table 1: An Alloy Composition (Alloy 1)
Ingredients Amount of Ingredients
(in wt%)
Fe 0.16
Si 0.858
Mg 0.766
Mn 0.787
Cu 0.10
Ti 0.015
Bi 1.64
Al 95.674
Total 100

[00042] METHOD OF PREPARATION OF ALLOY
[00043] About 10kg of pure Aluminium was taken in an electric resistance furnace and heated at about 660°C to obtain a melt of Aluminium. Melting of the Aluminium was followed by the addition of master alloys viz. Al-Fe5% (about 625 gm), AlSi10% (about 1677 gm) and AlMn10% (about 1538 gm) separately, into the melt of Aluminium at about 780 °C. After 15 mins, AlMg10% (about 1684 gm) master alloy was added to the above melt at about 740 °C. A master alloy, AlCu80% (about 24 gm) was added into the above melt followed by the addition of Al-5%Bi (about 7210 gm) after 10 mins of addition of AlCu80%. Finally, AlTi10% (about 35 gm) was added prior to casting. All the ingredients (master alloys) were added in stoichiometric amounts to attain the final melt composition as disclosed in Table 1. The final melt was mixed and held for 10 mins and degassed with Argon gas. Finally, the melt (having a temperature of ~700 °C) was poured into a preheated cast-iron mold after passing through a preheated (250 °C) ceramic foam filter. The final alloy was cast into 4” diameter cylindrical billets. The chemical composition final cast alloy was measured and confirmed using spectroscopy and wet chemical analysis.
[00044] To obtain the desired phases in the microstructure of the alloy, optimization of the homogenization process was done and the cast billets were then homogenized at 560 °C for about 6 hours followed by forced air cooling. An ultrasonic test of the billets was also conducted before extrusion to check for any casting porosity. Before extrusion, the billets were machined to remove the surface oxide layer. Extrusion of selected billets was done with the following parameters i) Pre-heating temperature of 480 °C to 500°C; ii) holding time of 2 hrs. After extrusion through a 25 mm diameter die the extruded profiles (alloy) were water quenched to retain the as-solutionized microstructure. The profiles were then sent for stretching and straightening up to ~1% and the rods were cut for ageing treatment at T6 temper condition. The extruded alloys were kept for natural ageing for 72 about hrs before artificial ageing was done at 175°C for about 6 hours.
After ageing treatment, alloy (samples) were machined according to the ASTM standard for the determination of the mechanical properties. Scanning Electron Microscopy (SEM) equipped with EDAX was used to study the phase morphology and elemental composition. Machinability characteristics were checked through surface roughness measurement. The properties of the alloys were determined using well known ASTM standard method.
PROPERTIES OF THE ALLOY - FUNCTIONAL RECIPROCITY OF THE ALLOY COMPOSITION
The alloy realized from the alloy composition in Table 1 above vis-à-vis the alloy being devoid of Bismuth element (commercially available) and the alloy comprising different amounts of Bismuth therein, were subjected to determination of specific potential properties, particularly, determination of machining properties along with other desired properties. Alloy compositions and properties whereof are provided herein-below in Table 2 and Table 3.

Table 2: Alloy of the present disclosure vis-à-vis the alloy being devoid of Bismuth element and the alloy comprising Bismuth element in different amounts
Alloy/Ingredients Fe Si Mg Mn Cu Cr Zn Ti Bi Pb Al
Alloy 1
(Present Disclosure) 0.16 0.858 0.766 0.787 0.10 _ _ 0.015 1.64 _ 95.674
Alloy 2
(Present Disclosure) 0.163 0.949 0.805 0.829 0.120 _ _ 0.014 1.82 _ 95.3
Alloy 3
(Commercially available alloy devoid of Bi) 0.200 0.852 0.755 0.761 0.004 0.0023 0.005 0.027 _ _ 97.3937
Alloy 4
(Commercially available alloy having Bi) <0.7 0.4-0.8 0.8-1.2 <0.15 0.15-0.4 <0.25 <0.25 <0.15 0.4-0.7 0.4-0.7 94-97%

Table 3: Properties of alloy corresponding to Table 2
Alloy/Properties Young Strength (YS)
(in MPA) Ultimate Tensile Strength (UTS)
(in MPA) Elongation
(in %) Machining Properties
Chip type Roughness after machining ((Ra in µm)
Alloy 1
(Present Disclosure) 319 341 15 Discontinuous 0.464
Alloy 2
(Present Disclosure) 318 344 16 Discontinuous 0.428
Alloy 3 260 310 8 Continuous 0.710
Alloy 4 220-240 240-260 8-10 Discontinuous 0.640- 0.700

As can be seen in Table 3 above, the alloy of the present disclosure affords dramatic improvement in machinability of the alloy while maintaining the strength (such as young strength, tensile strength, etc.) and other desired properties of the alloy as compared to the alloy being devoid of Bismuth element and the alloy comprising different amounts of Bismuth therein. Accordingly, it could be concluded that the alloy of the present disclosure when having Bi and Al as part of the alloy in the weight percentages as defined herein; exhibit exceptional functional reciprocity and affords dramatic improvement in machinability of the alloy while maintaining the other desired properties of the alloy.

ADVANTAGES
[00045] The present disclosure provides a lead and tin free Aluminium-Bismuth (Al-Bi) based alloy that may overcome one or more limitations associated with conventional Al based alloys.
[00046] The present disclosure provides a lead and tin free Al-Bi based alloy that exhibits improved machinability.
[00047] The present disclosure provides an Al-Bi based alloy that exhibits improved machinability while maintaining the strength (such as young strength, tensile strength, etc.) and other desired properties.
[00048] The present disclosure provides an Al-Bi based alloy that exhibits functional reciprocity.
[00049] The present disclosure provides an Al-Bi based alloy that is economical and easy to prepare.
[00050] The present disclosure provides a method of preparation of an Al-Bi based alloy with improved properties.
, Claims:1. A lead and tin free alloy composition, said composition comprising: 0.1 to 0.2 wt% of Fe, 0.70 to 1.0 wt% of Si, 0.55 to 0.85 wt% of Mg, 0.6 to 0.90 wt% of Mn, 0.05 to 0.20 wt% of Cu, 0.01 to 0.03 wt% of Ti, 1.55 to 1.95 wt% of Bi, and the rest being Al.

2. The alloy composition as claimed in claim 1, wherein the composition comprises: 0.1 to 0.2 wt% of Fe, 0.70 to 1.0 wt% of Si, 0.55 to 0.85 wt% of Mg, 0.6 to 0.90 wt% of Mn, 0.05 to 0.20 wt% of Cu, 0.01 to 0.03 wt% of Ti, 1.60 to 1.90 wt% of Bi, and the rest being Al.

3. A lead and tin free alloy comprising: 0.1 to 0.2 wt% of Fe, 0.70 to 1.0 wt% of Si, 0.55 to 0.85 wt% of Mg, 0.6 to 0.90 wt% of Mn, 0.05 to 0.20 wt% of Cu, 0.01 to 0.03 wt% of Ti, 1.55 to 1.95 wt% of Bi, and the rest being Al.

4. The alloy as claimed in claim 1, wherein the alloy comprises: 0.1 to 0.2 wt% of Fe, 0.70 to 1.0 wt% of Si, 0.55 to 0.85 wt% of Mg, 0.6 to 0.90 wt% of Mn, 0.05 to 0.20 wt% of Cu, 0.01 to 0.03 wt% of Ti, 1.60 to 1.90 wt% of Bi, and the rest being Al.

5. The alloy as claimed in claim 1, wherein the alloy exhibits surface roughness after machining in the range of 0.4 to 0.6 µm Ra.