In the metal manufacturing industry, mechanical properties play a huge role when choosing the right alloy for each job. Throughout casting and machining processes, as well as during the product's useful life, the chosen material will be subject to many external forces. It’s up to the manufacturers to create products that perform as needed every step of the way. By understanding mechanical properties, manufacturing professionals can make the right choices for materials and processes.

Mechanical properties describe how a material responds to applied loads or forces. These properties are not constant; they change based on temperature and other external factors, so manufacturers must have a full understanding of the operating environment of a part before recommending an appropriate material. Key mechanical properties of metals include:

• Strength
• Ductility and Malleability
• Weldability
• Toughness
• Fatigue Resistance
• Hardness

Physical properties are another way of distinguishing metals. You can learn more about physical properties in our blog post here.

Strength

Strength can be measured in a number of ways, but generally represents how much force an object can withstand without bending or breaking. Strength-to-weight ratio is a key property of metals, because it tells manufacturers how much material must be used to meet a specific strength requirement.

Strength is often measured in terms of a material’s response to stresses, or applied forces, in three configurations: compression, tension and shear. Compression involves forces directed toward the object’s center point, tension pulls the material apart, and shear forces act parallel to each other but in opposite directions.

Learn more about the strength of metals in our "Metal Properties: Strength" blog post.

Ductility and Malleability

While strength is often a good predictor of real-world performance, manufacturers need to push materials beyond their limits to form new shapes. Ductility and malleability indicate how easily a material can be manipulated without breaking. Ductility refers to a material’s response to tensile stress, or its ability to be stretched, rolled or extruded without breaking. Malleability refers to compressive stress, as in flattening. Aluminum’s high malleability is why it’s so widely used to make thin foil.

Since a material’s behavior changes depending on the temperature, a metal might have good ductility or malleability at high temperatures, but poor ductility or malleability at room temperature. Hundreds of years ago, blacksmiths were already aware of this variable, and heated iron-based products until glowing before hammering them into shape.

Learn more about metallic ductility in our "Metal Properties: Ductility" blog post.

Weldability

Weldability is the ability of a material to be welded and, more specifically, the science of knowing the environment, process and materials required for a successful weld. When we say successful, we are referring to a weld that exhibits necessary material properties and performs as expected in the field.

Understanding the weldability of various alloys is key to creating welds that last and parts that perform in the field. As a mechanical property, weldability is also an important consideration in designing and producing cast parts. With weldability protocols in place for individual each alloy, metal casting companies can perform welds that ensure welded parts are indistinguishable in their field performance from non-welded parts.

Learn more about weldability in our "Metal Properties: Weldability" blog post.

Toughness

Toughness measures the amount of energy a material can withstand, or absorb, before fracturing. In the context of other mechanical properties, toughness for steel products represents a balance between strength and ductility.

As a material term, toughness can sometimes cause confusion: two very different materials can both be considered tough. For example, an iron anvil is tough because its strength is very high, and it resists fracture by maintaining its material integrity thanks to its strength. On the other end of the spectrum, silly putty is also a tough material, not because it’s strong but because it’s very ductile and will resist fracture until you pull it far enough apart that the two ends separate. Anvils and silly putty are very different, but they’re similar in that they are both tough, and they both absorb a good deal of energy before fracturing.

In the real world, most metal products need to be somewhere on the spectrum between the anvil and the silly putty. That means that for foundries and other manufacturers working with steel, optimal toughness means a balance between strength and ductility. The toughness of a material can vary markedly for different alloys, even those with similar chemical compositions or heat-treatment recipes. Toughness also varies within the same alloy under different testing conditions. For example, operating temperature augments toughness, as does speed of loading (the speed at which a loading force is suddenly applied to the material).

Learn more about toughness in our "Metal Properties: Toughness" blog post.

Fatigue Resistance of Metals

In real-world applications, metal parts often undergo repeated stresses over a long period of time. While none of these stresses, taken individually, would challenge the part’s strength, ductility or toughness, the repetition itself can lead to failure. In fact, according to the International Journal of Fatigue, fatigue contributes to approximately 90% of mechanical failures.

Fatigue resistance is a measure of a part’s ability to undergo repeated, cyclical stress without fracturing or permanently deforming. Amounts of stress close to the material’s limit will result in earlier fatigue failure, compared to lower amounts of stress. Like other mechanical properties, the fatigue resistance of a given alloy depends on the temperature at which the stress is applied, as well as other environmental factors.

The fatigue resistance of a final part depends not only on its material makeup, but also on the presence of defects. Issues like porosity, cracking or other flaws caused during manufacturing can drastically reduce the fatigue resistance of a part. For more insights on common casting defects and ways to prevent them, read our blog post, "Understanding Casting Defects: When Is a Casting Returnable?"

Learn more about fatigue resistance in our "Metal Properties: Fatigue Resistance" blog post.

Hardness

Hardness in materials can refer to performance across a number of parameters, including resistance to deformation, resistance to scratching or resistance to cutting. Metals show a strong correlation between tensile strength and hardness, and hardness can often be increased in steel by increasing its percentage of carbon.

Hardness can be measured in many ways, and the Brinell Hardness Test is one of the most common for metal products. The test, first proposed in the year 1900, involves pressing a sphere made of carbide or hardened steel into the surface of the part being measured. The resulting indentation on the surface is then measured using a microscope, and the Brinell Hardness Number (BHN) is given as the load divided by the surface area of the indentation.

Harder alloys are often less machinable, which can create obstacles when manufacturing products. When taking Design for Manufacturability into account, it is sometimes better overall to use a less hard alloy for a casting, especially if the product will undergo extensive machining at a later stage.

Learn more about mechanical hardness in our "Metal Properties: Hardness" blog post.

Choosing the Right Alloy Based on Mechanical Properties

In the world of manufacturing, the most important mechanical properties depend on the product's intended use. Since mechanical properties vary with the environment, the product design process must include a thorough analysis of the environment in which the product will perform, including temperature, moisture and load requirements. Manufacturers also must consider all forming processes the material will undergo before emerging as a final product. Often, engineers and metallurgists are tasked with finding a balance between performance metrics like strength, and process metrics like machinability.

An APQP process can ensure that all relevant variables have been considered before choosing an alloy, and the best foundries follow APQP procedures throughout product design. To learn more about optimal product design steps in metalcasting & CNC machining, read our dedicated blog series on product design and development.

Learn more about metal properties and their applications in metalcasting and cnc machining with our free ebook: