1. Introduction
The term non-ferrous alloys are used for those alloys which do not have iron as a base element. Generally, the non-ferrous alloys commonly used in engineering application are based on aluminium, copper, magnesium, titanium etc. The microstructures of these non-ferrous alloys are highly diversified in nature and are dependent on their composition and processing method. Understanding of these microstructures is crucial for tailoring material properties for specific applications in aerospace, automotives, and electrical industries.

The advantages of Non-ferrous alloys over ferrous alloys are as follows:

• Good resistance to corrosion without special processes having to be carried out.
  
• Low density and are hence used in manufacturing light weight components.
  
• Manufacturing is easier as casting can be done because of their lower melting point.
  
• Feasibility to be cold worked, as they possess FCC crystal structure and hence greater ductility.
  
• Higher thermal and electrical conductivities.
  

The mechanical properties of non-ferrous materials can be improved by using different types of heat treatment such as solution treatment, ageing, and precipitation hardening. Besides, they also possess features such as, high-temperature properties, oxidation and corrosion resistance, biocompatibility, thermal conductivity, and electrical conductivity.

2. Aluminium and its Alloys:

Figure 1. Optical microstructure of (a) annealed aluminium (b) rolled aluminium.

Aluminium, with its rich abundance of 8% on the earth's surface, finds extensive applications in various industries across the globe. It is indeed the third most abundant element on the earth. Aluminium and its alloys possess advantages including superior corrosion resistance, light weight properties, excellent machinability, good thermal and electrical conductivity, and high ductility. The pure form of Al is extracted from its most common ore, bauxite.

Heat treatment is an important tool used to modify the microstructure of the aluminium alloys.
Among different heat treatments, age-hardening is the most common process used for improving the mechanical properties of aluminium-4.5% Copper alloy system. Aluminium alloys find application in the fields of building/construction, packaging containers, transportation, electrical conductors, machinery/equipment’s, etc. Microstructure of aluminium depends highly on the processing method as well as the alloying elements, such as copper, magnesium, and silicon. On adding these elements, various types of phases are formed in the microstructure.

2.1 Al-Cu Alloys
These alloys typically comprise an FCC matrix with small copper-rich precipitates (e.g., Al2Cu) dispersed throughout. These precipitates provide strength through precipitation hardening.

2.2 Al-Mg Alloys
Aluminium-magnesium alloys have hexagonal close-packed (HCP) crystal structures, providing excellent strength and corrosion resistance.

2.3 Al-Si Alloys
Aluminium-silicon alloys have a dendritic microstructure, with silicon forming discrete particles within the aluminum matrix, enhancing its wear resistance and castability.

Figure 1 shows two different types of microstructures of aluminum in annealed and rolled conditions. Figure 1(a) shows the microstructure of the aluminum in an annealed condition characterized by larger grains with distinctive grain boundaries. Annealing is a typical heat treatment used to relieve the presence of any internal stresses in the microstructures and thereby improve the mechanical properties of the alloy system. This improves the ductility and formability of the aluminum alloy by annihilating the dislocations. This heat treatment makes aluminum alloys for meeting specific applications, including aerospace, automotive, and construction applications, where light weight, corrosion resistance, and enhanced foamabilities are the most widely used properties. Figure 1(b) shows the rolled aluminum microstructure characterized by distinctive grain structural alignments resulting from rolling. Rolling operation elongates the grains along the rolling directions due to the application of mechanical forces during the rolling operations. This type of rolling operation produces preferred textures within the microstructures. The dislocation density in rolled aluminum is relatively high and causes an increase in the strength of the material. In summary, rolled aluminum exhibits a microstructure characterized by elongated and aligned grains along the rolling direction, forming a distinct texture. The alignment of grains, coupled with the reduction in grain size and the presence of dislocations, imparts specific mechanical and anisotropic properties to the material, making it suitable for various applications where strength, lightweight construction, and formability are essential considerations.

3. Copper and its Alloys:
Figure 1 shows two different types of microstructures of aluminum in annealed and rolled conditions. Figure 1(a) shows the microstructure of the aluminum in an annealed condition characterized by larger grains with distinctive grain boundaries. Annealing is a typical heat treatment used to relieve the presence of any internal stresses in the microstructures and thereby improve the mechanical properties of the alloy system. This improves the ductility and formability of the aluminum alloy by annihilating the dislocations. This heat treatment makes aluminum alloys for meeting specific applications, including aerospace, automotive, and construction applications, where light weight, corrosion resistance, and enhanced foamabilities are the most widely used properties. Figure 1(b) shows the rolled aluminum microstructure characterized by distinctive grain structural alignments resulting from rolling. Rolling operation elongates the grains along the rolling directions due to the applications of mechanical forces during the rolling operations. This type of rolling operation produces preferred textures within the microstructures. The dislocation density in rolled aluminum is relatively high and causes an increase in the strength of the material. In summary, rolled aluminum exhibits a microstructure characterized by elongated and aligned grains along the rolling direction, forming a distinct texture. The alignment of grains, coupled with the reduction in grain size and the presence of dislocations, imparts specific mechanical and anisotropic properties to the material, making it suitable for various applications where strength, lightweight construction, and formability are essential considerations.


Figure 2. Microstructure of (a) annealed copper and (b) rolled copper.

Copper is essential for modern living. It delivers electricity and clean water into our homes and cities and makes an important contribution to sustainable development. More than that, it is essential for life itself. Copper is a mineral and an element known as naive copper. It is an industrial metal used mostly in the unalloyed and alloyed conditions. It is extracted mostly from the ores of chalcopyrite, chalcocite, and cuprite. Copper and its alloys are well known for their higher ductility and formability, excellent electrical and thermal conductivity, ease of alloying additions, good antimicrobial properties, anti-fouling properties, excellent range of colours, higher durability, better weldability, recyclability, availability, and sustainability. Alloying additions and processing are excellent sources of altering the microstructures of copper. Copper usually has three important alloys known as: Cupro-Nickel, Brass, and Bronze. Brass is an alloy of copper and zinc whereas Bronze is an alloy of Copper and Tin. Finally, cupronickel is an alloy of copper and nickel. Copper finds applications heavily in the electrical industries due to their higher electrical conductance, plating on different components, and other applications in form of brass and bronze alloys. Figure 2 (a) shows the microstructure of annealed copper whereas Figure 2 (b) shows the microstructure of rolled copper. Microstructure of annealed copper is characterized by larger, equiaxed grains, reduced dislocation density, and improved ductility and electrical conductivity. In addition to that copper also forms annealing twins in its microstructures during annealing. Annealing is a crucial process in the production of copper products for various industries, including electronics, construction, and transportation, where the desirable properties are softness, malleability, and high conductivity. Formation of annealing twins within the microstructure of copper can be explained by the atomic rearrangements and defect migrations, such as dislocations in the crystal lattice during annealing process. Twin formation reduces the overall energy of the system and relieves the stresses. Figure 2(b) shows the microstructure of the rolled copper that shows the presence of preferred textured orientation of grains along the rolling directions within the microstructure. It improves strength, mechanical hardness, reduces ductility. Furthermore, the degree of enhancement of the mechanical properties during rolling depends on the degree of deformation, initial rolling parameters, and initial conditions in copper. These factors affect the applications of copper including construction, electrical engineering, and manufacturing.
4. Brass and Bronze

Figure 3. Microstructure of (a) 70-30 brass, (b) 60-40 brass, (c) Bronze.

Brass is an alloy of copper and zinc, whereas bronze is an alloy of copper and tin. Copper-zinc alloys, known as brass, exhibit a two-phase microstructure. They consist of an alpha phase (copper-rich) and a beta phase (zinc-rich). The proportions of these phases determine the alloy's properties. Brass is obtained in different forms. Such as alpha brass (with 36% zinc) and alpha-beta brass. Brass is also found in two essential forms known as 60-40 brass and 70-30 brass. In 60-40 brass, 60 wt.% is the percentage of copper, and 40wt.% is the weight percentage of zinc. Brass contains zinc as the principal alloying element. Brass is mainly categorized into three different types: (1) Cu-Zn alloys, (2) Cu-Pb-Zn alloys or leaded brasses. (c) Cu-Zn-Sn alloys or tin brasses. Brasses have high corrosion resistance, and are readily machinable. They also acts as good bearing materials. Zinc in the brass increases the ductility along with strength. Brass possesses greater strength than copper. However, it has a lower thermal and electrical conductivity. Types of brass are discussed below:
4.1 Alpha brass
Brasses with up to 36% Zn are known as Alpha Brasses. Depending on Cu content,they are categorized into Yellow α brass and Red α brass.

4.1.1 Red α Brass
The brasses with 5-20% Zn content are known as Red α Brasses. Due to their better corrosion resistance, they do not observe any dezincification or season cracking. Some of the alloys under this category are discussed below.
* Gliding Metal: Gliding metal is an alloy containing 5% Zn and possesses shades of colour from red to brassy yellow. It is used for making coins, medals, tokens, fuse caps, etc.
* Commercial Bronze (90Cu-10 Zn): Commercial Bronze possesses excellent cold and hot working properties. It is used in making costume jewellery, lipstick cases, etc.
4.1.2 Yellow α Brass
Yellow α brasses contain 20 to 36% Zn. They exhibit good strength and ductility, making them suitable for drastic cold working, Season Cracking, and Pitting corrosion. Cartridge brass (70Cu-30Zn) and yellow brass (65Cu-35Zn) are some widely used yellow α brass alloys. Typical applications for these alloys include automotive inner parts and plumbing components. The addition of 0.5 to 3% of Pb improves the machinability of these alloys. Some of the alloys of the Yellow α Brass category are discussed below:
* Cartridge Brass: Cartridge Brass contains 70% Copper and 30% zinc. Cartridge brass is well-known for its excellent cold-working and forming properties. It is a popular choice for various applications, including producing plumbing components and musical instruments like trumpets and trombones. The alloy's good combination of strength, corrosion resistance, and malleability makes it suitable for these applications. Figure 3(a) shows the microstructure of 70-30 brass characterized by a two-phase structure consisting of an alpha (α) phase rich in copper and a beta (β) phase rich in zinc. This combination of phases gives 70-30 brass desirable properties, such as a balance between corrosion resistance and strength, making it suitable for various applications, including cartridge casings, plumbing components, and musical instruments. The specific microstructure and properties of the alloy can be further tailored through processing and heat treatment techniques to meet various application requirements.
* Admiralty Brass: The alloy with Cu 71%, Zn 28%, and Sn 1% is referred to as Admiralty Brass. It is used for the tubes and other parts of the condenser which are cooled by fresh water, and for many other purposes.
* Aluminium Brass: An alloy with 76% Cu, 22% Zn, and 2% Al. A minor amount of arsenic is added to inhibit dezincification in the alloy system.
4.2 Alpha – Beta Brass
The brasses which contain more than 36% of Zn form duplex microstructures with Cu-rich α phases and Zn-rich ß phases. They are thus known as Alpha Beta Brasses. Some of the commonly used α-ß brasses are listed below.
* Muntz Metal or Yellow Metal: Muntz Metal contains 60% of copper and 40% of zinc and is essentially a hot working material. It is used in ship sheathing, perforated metal, valve stems, condenser tubes, architecture works, ammunition casings, etc. The microstructure shown in Figure 3(b) shows the microstructure of this brass. The 60-40 brass microstructure is characterized by a two-phase structure consisting of an alpha (α) phase rich in copper and a beta (β) phase rich in zinc. This combination of phases gives 60-40 brass desirable properties, such as corrosion resistance, electrical conductivity, and good machinability. The specific microstructure and properties of the alloy can be further tailored through processing and heat treatment techniques to meet various application requirements.
* Naval Brass (60Cu-39.25Zn-0.75Sn): Naval brass, also known as Tobin bronze, is used for marine purposes. This alloy has increased resistance to saltwater corrosion. The addition of Pb improves machinability.
* Manganese Bronze (58.5Cu-39Zn-1.4Fe-1Sn-0.1Mn): The alloy has high strength and excellent wear resistance.
* Cast Brass: Cast alloy consists of white needles of α in a matrix of β. Many other alloying elements are present in the alloy including Tin 1 to 6% and Pb 1 to 10% with Fe, Ni, Al. Leaded red brass (85Cu-5Sn-5Pb-5Zn) is an example of cast brass. Used for fair strength and good machinability properties.
Bronze is an alloy of copper and tin that can contain upto 12 wt.% of alloying elements. It typically consists of copper (Cu) as the base metal, with the addition of other elements such as tin (Sn), aluminium (Al), silicon (Si), and sometimes other elements like phosphorus (P) or manganese (Mn) in varying proportions. The specific composition of bronze can vary widely, leading to a range of alloys with different characteristics. Its unique combination of properties, including strength, corrosion resistance, and malleability, has made it a valuable material for both functional and artistic purposes throughout human history. An alloy of copper and elements other than nickel or zinc, bronze is basically an alloy of copper and tin. It possesses superior mechanical properties and corrosion resistance than brass. It is comparatively hard, and it resist surface wear. It can be rolled into wire, rod, and sheets. Bronze finds its suitable applications in musical instruments, marine equipment, bearings and bushings. There are numerous types of bronze alloys, each with its unique properties. Some common types include phosphor bronze (Cu-Sn-P), aluminium bronze (Cu-Al), silicon bronze (Cu-Si), and manganese bronze (Cu-Mn). These alloys are tailored for specific applications based on their properties. Phosphor Bronzes, or tin bronzes, are alloys containing copper, tin and phosphorous. The phosphor bronzes contain between 0.5 and 11% tin and 0.01 to 0.5 % phosphorous. High strength, toughness and corrosion resistance are some of its unique properties. Silicon bronze consists of 1-4% Si,0.5-1.0% Iron, 0.25-1.25% Mn, and balance amount of copper. When lead added as 0.05% improves machinability. It possesses high strength and toughness as that of mild steel and corrosion resistance as that of copper Bronzes are the strongest work hardenable Cu alloys compared Mild steel, and possess better corrosion resistance compared to that of copper. These alloys are used for tanks, pressure vessels and marine construction. Aluminium bronze usually consists of 89% Cu, 7% Al, and 3.5% Sn, 4 to 11% Al . Among other elements, Fe (0.5 to 5%) increases strength and hardness by grain refinement, Ni (up to 5%) has same effect as Fe but to a lesser extent, Si (up to 2%) improves machinability, possesses good strength, high corrosion resistance, good heat resistance, good cold working. Aluminium bronzes are copper alloys with up to 11% aluminium, display high strength at elevated temperatures and very good corrosion resistance. They are suited for marine propellers, highly stressed rotors for pumps and water turbines, and bearings and parts for the chemical industry. Copper-aluminium wrought alloys are used in mechanical and light engineering. Figure 3(c) shows the microstructure of Bronze consists of α-matrix phase rich in copper and this phase improves ductility, malleability, and electrical conductivity of the material. Presence of β-phase is evident in the form of black areas within the microstructure which is responsible for improving the overall strength of the alloy system.

5. Titanium and its Alloys

Figure 4. Microstructure of Titanium alloys at different magnifications (a)-(d).

Titanium and its alloys are well known for their unique properties and applications. Ilmenite and Rutile are the common ores from which titanium is extracted using Kroll’s process. Their exceptional strength-to-weight ratio, higher corrosion resistance, biocompatibility, higher melting point, enhanced ductility, and formability makes them suitable candidates for applications in aerospace and aviation (airframes and engines), medical implants (knee and hip joint implants made of Ti-6Al-4V) and healthcare services, sporting goods, propeller shafts, chemical processing industries (due to its excellent corrosion resistance). Titanium and its alloys catch fires easily, which is a problem for this alloy, in addition to the higher cost due to expensive extraction of Titanium. Figure 4 (a)-(d) shows the lamellar morphology of alpha and beta phases in Widmanstätten form found in the microstructures in the case of titanium alloys. the microstructure of titanium is primarily characterized by the alpha phase with an HCP crystal structure in its pure form. The presence of other phases, like beta or intermetallic phases, depends on alloy composition and processing conditions. The microstructure and properties of titanium can be tailored to meet specific application requirements through alloying and heat treatment processes.