What Are The Softest Metals? Properties, Types, & Uses

Softest metals

The marvels of materials that can be cut by a knife, be CNC machined effortlessly, and be applicable for conductivity yet very light are attributed to the softest metals. Contrary to what comes with the harder and more common metals, soft metals bend, form, and conduct electricty with amazing ease. 

Caesium, lead, aluminum, and gold are some of the metals in this special category. But are all suitable for your CNC machined parts? Some of these metals are highly reactive, but it is the luster, malleability, and low weight that suit CNC machining projects. 

The melting point, corrosion resistance, and chemical stability of these metals vary, so their use as alloying elements for crucial metals are subject to expert involvement. The subsequent manufacturing of the alloys is also better handled by professionals. 

Get all the CNC machining services you need for the softest metals from ProleanTech. In this article, we share insightful details about the softest metals, including their properties, applications, and processing options. 

Let’s analyse these special materials together!

What metal Is Soft? 

A soft metal refers to a type of metal that is easy to form or bend owing to its high malleability and limited hardness. This is interesting because naturally, metals are associated with rigidity and strength. Yet, some metals are highly soft, thus considered the softest metals.

The easy workability of soft metals can definitely interest a product engineer. However, that’s not the only property of soft metals. They are also conductive and reactive, among other properties, but these vary for specific soft metals. Therefore, there are some considerations to make when choosing a soft metal to use. 

Soft metals have unique atomic structures that make them behave the way they do. The softest metal, Cesium for instance, noticeably has a large atomic size. The distance between the nucleus and the outermost electron is relatively big for this metal. 

On the periodic table, some of the softest metals are found on the first column. These materials are so soft that a knife can easily cut through them. So, metals such as sodium (Na), Lithium (Li), francium (fr), and potassium (K) are also in this category. 

However, it is important to distinguish between alkali metals and soft metals. All alkali metals are soft metals, but the reverse is not necessarily true. Some metals – gold, lead, and others – are not alkali metals, but are very soft. 

The important distinction here is that the softness of a metal largely refers to the mechanical properties such as high malleability and low yield strength. 

Caesium – The Softest Material In The World

Caesium 

Caesium (Cs) is renowned for its remarkable softness, so much that you could effortlessly cut it using a kitchen knife at room temperature. It is an extremely reactive material that explodes in water and ignites in air. 

This alkali metal, whose discovery is attributed to Robert Bunsen and Gustav Kirchhoff in 1860, is typically silvery white and melts at 28.4° C. That means in some environments, it is already in liquid form. 

Since caesium is extremely electropositive and reactive, it is usually stored and carried in vacuum, inert atmosphere, or dry saturated hydrocarbons. 

Expert use of the material is found in petroleum exploration, electric power generation, medical applications, and electronics.

Despite these uses, caesium is very different from other soft metals such as aluminum, gold and copper. Major disparities are in the extreme softness and reactivity, properties which make normal machining and processing impossible for the alkali metal. 

The Chemical Properties Of Soft Metals

Soft metals are usually associated with low melting points and reactivity as the main chemical properties. These are important insights that can help manufacturers using these metals determine the exact one to use for a chemical environment.  

Here is a table summarizing the chemical properties of the softest metal.

Physical Properties Of Soft Metals

High ductility and low tensile strength are notable physical properties of the softest metals. When subjected to stress, these metals exhibit these and other physical properties that interest and guide manufacturers on what material to use for a project. 

They are critical insights because some of the relevant manufacturing techniques such as CNC machining and forming must look into these properties. 

What Are The 10 Softest Metals?

We already mentioned some soft metals but are they the softest you can get? Cesium is obviously on top of the list of the 10 softest metals, but some of the other softest metals are gold, lead, cadmium, mercury, brass, and zinc. 

The metal you pick for your project should depend on the mechanical and other specs because these determine how well it blends in an assembly of CNC machined parts. 

Here is a brief about the 10 softest metals according to the metal softness chart and real-life experience in the field.

• Gold 

The perennial economic value aside, this soft metal is also highly conductive, malleable, corrosion resistant, and ductile. Some high-reliability contacts in the electronic industry are made from this metal.

Gold bars

• Brass 

The mixture of dimensional stability and strength of this soft metal is valuable in some CNC machined parts and components. Brass has a sparklng finish, which combines perfectly with easy machinability for products like decorations and plumbing fittings. 

Brass plate

• Zinc 

Zinc has a low melting point, but it is not as soft or malleable as some of the other soft metals, unless heated. 

Zinc plates

• Aluminum 

Aluminum is one of the major soft metals. It is light, corrosion resistant, versatile, and easy to machine. These properties make it one of the most used soft metals. Some grades of the metal are strong enough to be used reliably in aerospace and other critical sectors. 

Aluminum rolls

• Bronze 

When copper and tin are combined, they make bronze, a relatively harder metal than copper. The addition of tin enhances the hardness of the metal to make it suitable for pumps, gears, and such components. 

Bronze parts

• Magnesium 

As one of the most abundant elements on Earth, magnesium does get consideration in various applications. However, its relative reactivity is a challenge in the CNC machining space. It is whitish, soft, and lightweight. 

Magnesium ingots

• Lead

Lead is another malleable and ductile soft metal, but it is relatively dense. Its most popular applications are in lead-acid batteries and radiation shielding. Note that the material is toxic, so not suitable for regular niches. 

Lead ingots

• Tin 

The corrosion resistance and low melting point of tin is an important property for metal coatings. The soft metal is also widely used in alloys for soldering purposes. 

Raw tin metal

• Silver 

Silver is another very soft metal with numerous industrial applications. It is considered a precious metal for its jewelry and tableware applications, but beyond that, it helps make excellent grinding wheels and electronic equipment. 

Silver

• Copper

Copper has superior thermal and electrical conductivity. In CNC machining projects, copper parts and components are perfect in circuits and heat sinks, where these properties are necessary. 

Copper tubes

It is important to note that some of the softest materials in the world can deform at the slightest pressure. These are impractical in CNC machining or related engineering processes. Examples are caesium and rubidium. 

Metal Softness Chart

For a better understanding of the softness and suitability levels of the softest metals, here is a metal softness chart covering Mohs hardness, softness, and machinability. 

The Main Applications Of Soft Metals 

There are many uses of soft metals across different fields, from jewelry to electrical wiring, and shielding to soldering. If you are in luxury products, electronics, plumbing, or such fields, CNC machined items from these unique metals can make a lot of sense. 

Electricals And Electronics

For products in this area, electrical conductivity is a core characteristic. It is easy to achieve this plus other benefits from soft metals like copper and gold. 

Jewelry

Copper and gold make beautiful valuable ornaments that rule the jewelry industry. To add to the ease of machining, these materials are highly regarded for their aesthetic value.

Gold jewelry

Plumbing 

Copper is a popular metal in plumbing and HVAC systems. Engineers in these areas give the material priority for its ease of machining and corrosion resistance. 

Marine Equipment 

Bronze is a popular material for marine equipment, primarily due to its high corrosion resistance. Popular devices made from this soft metal are valves and pumps. 

Musical Tools 

Some soft metals have great acoustic properties. Combining that with machining ease, for instance, for brass, makes excellent options for musical equipment. 

These and many other applications of the softest metals can be actualized with quality CNC machining services. Get your quote now!

How to Choose The Best Soft Metal To Use

There is so much to get from the softest metals depending on your project requirements. Are you looking for malleability, corrosion resistance, or a specific strength level? Consider soft metal options as advised by the best team in CNC machining and sheet metal fabrication services.

These are some of the points to consider for this decision:

1. Chemical stability
2. Mechanical properties
3. Achievable surface finish
4. Machinability 
5. Oxidation behavior 
6. Dimensional stability 

How To Process Soft Metals: CNC Machining And Others 

Like other metals, soft metals can be manufactured through conventional or advanced methods. For instance, modern CNC machining techniques can produce quality parts and components from gold, lead, and other soft metals. 

Other processing methods for the softest metals are forging and stamping. Some in the DIY areas have also designed ways of using manual techniques to craft items from the metals. Each of these methds has its strengths and drawbacks, so you have to decide. 

CNC Machining For Soft Metals

Soft metal’s machining ease and suitable properties for many applications make them popular in CNC machining processes. When you require complex and reliable parts from these materials, you can always consider CNC machining as a top source. 

The malleabilty of these materials is especially excellent with CNC milling, drilling, sheet metal fabrication techniques, and turning processes, allowing for easy manufacture of a broad range of parts. Some CNC machinable soft metals include aluminum, brass, and copper. 

CNC machined copper part

Forging The Softest Metals

Soft metals such as copper and aluminum can be forged. The benefit of using this manufacturing method is the minimal wastage involved, considering some of the softest metals are very valuable and pricey. 

Often, the resulting forged part has higher strength and fatigue resistance than the raw material. 

Stamping For Soft Metals

Stamping, the process of generating specific shapes from flat material, is also applicable for some soft metals – aluminum, copper, and others. The malleability of these metals make this manufacturing method possible and adds to the versatility of parts from soft metals. 

Further reading: CNC Machining Complete Guide

Conclusion 

Soft metals like caesium, aluminum, and gold have a special blend of malleability, electrical conductivity, and other exciting chemical and mechanical properties that make them very versatile. Their CNC machined parts are suitable for many applications where conventional metals may not help. 

Understanding these and other aspects of the softest metals helps manufacturers, dealers, and end users specify the exact material they require for their parts and components. 

As we gear into the future and more product innovations emerge, the relevance of the softest metals can only increase. Your CNC machining requirements involving these materials are at home with ProleanTech. 

 Contact us today for all your custom machining needs. Don’t forget to visit our blog section often for more tips and insights to take your precision machining and fabrication projects to the next level. 

Faqs 

What metal is super soft?

Cesium, with a Mohs Hardness of approximately 0.2 is a super soft metal.