Yield strength is the stress point at which an aluminum alloy begins to deform irreversibly and cannot return to its original shape. Tensile strength is the maximum tensile force an aluminum alloy can withstand before breaking. Yield strength is used to set safe load limits, while tensile strength is key to dealing with parts that are subjected to extreme tensile forces, such as fasteners, frames, or joints.
This article explains yield strength and tensile strength through stress-strain curves, differences, test methods, influencing factors, alloy data, and practical selection strategies. Let’s read on to make scientific and practical aluminum alloy die casting material decisions for your next project.
Interpretation of Stress-Strain Curves
Transition from the Elastic to the Plastic Stage
From point O to A, the material deforms elastically in proportion to Hooke’s law.
When point B is reached, it enters the yield stage (B to C) and begins to deform plastically.
After point C, the material no longer returns to its original shape and enters the irreversible deformation stage.
Yield Behavior and Work Hardening
Point C is the upper yield point, and point D is the lower yield point, which is the yield strength of the material.
As the strain increases, the material enters the work-hardening zone, and the strength increases due to dislocation interaction.
During this stage, the material becomes temporarily stronger until it eventually breaks.
Ultimate Strength and Fracture
Point E is the peak of the curve, corresponding to the ultimate tensile strength, which is the maximum stress that the material can withstand.
After that, necking occurs, and the cross-sectional area becomes smaller, resulting in local stress concentration.
Point F is the fracture point at which the material completely breaks and loses its load-bearing capacity.
Yield Strength: The First Line of Structural Defense
Definition
The yield strength is the critical stress value at which the material begins to produce irreversible deformation.
Before this point, the material deformation is elastic and can be fully recovered; after exceeding it, it enters the plastic deformation stage, and the material will no longer return to its original state.
Importance
Maintaining stress below the yield strength helps prevent permanent deformation caused by load, thermal expansion, or impact.
This is crucial to maintaining the dimensional stability of the structure for a long time.
Therefore, the yield strength is usually used as the lower limit of the “safe load-bearing capacity” in design evaluation.
Design Purpose
In engineering design, a safety factor ranging from 1.5 to 3 times is usually set according to the load uncertainty and the working environment to ensure that the actual force on the material is far below the yield point.
This approach can effectively deal with the risk of structural deformation caused by long-term use, fatigue load, or accidental impact.
Tensile Strength: The Ultimate Limit Before Fracture
Definition
Tensile strength is the maximum tensile stress that a material can withstand before it completely breaks, and is a key parameter for judging the ultimate bearing capacity of a material.
Unlike yield strength, it usually has no warning, and overloading will directly lead to material fracture.
Application Impact
In key parts that are subjected to high tensile stress, such as fasteners, connecting frames, suspension arms, or safety guards, tensile strength determines the integrity of the part structure under extreme conditions.
Once the strength is insufficient, it may cause a fracture accident, failing the entire structure.
Safety Significance
Yield strength is used to prevent deformation, while tensile strength is the last line of defense to avoid fracture.
Especially in the presence of impact, overload, or emergency conditions, the rational selection of high tensile strength alloys can significantly reduce the risk of sudden fracture and ensure the stability of the key component structure.
Key Differences Between Yield Strength and Tensile Strength
|
Features |
Yield Strength | Tensile Strength |
|
Definition |
Stress where permanent deformation begins | Maximum stress before fracture |
|
Position on Curve |
Before UTS, the start of plastic deformation | Peak of the curve, before necking |
| Purpose in Design | Prevents shape loss and dimensional inaccuracy |
Prevents catastrophic breakage under extreme load |
| Application Sensitivity | Precision parts, frames, and housings |
Fasteners, load paths, emergency-stress zones |
| Failure Indicator | Gradual change, visible deformation is possible |
Sudden failure without warning |
Method for Measuring the Strength of Aluminum Alloys
Testing Process
The yield strength and tensile strength of aluminum alloys are usually obtained through tensile tests.
In the test, the standard specimen is uniformly stretched to fracture, and the load and elongation data are recorded at the same time.
The stress-strain curve drawn from this can intuitively display the elastic range, yield behavior, maximum load capacity, and fracture point of the material.
Yield Point Determination
Because the yield zone of aluminum alloys has a smooth transition, the 0.2% offset method is often used to determine the yield strength.
This method translates the slope of the elastic segment by 0.2% strain, and the intersection is the yield point.
This method unifies the definition of yield strength and makes different materials and batches comparable.
Testing Standards
Testing is generally performed according to ASTM E8 or ISO 6892 standards, both of which have clear specifications for specimen shape, clamping length, loading rate, and test temperature to ensure a consistent testing process and accurate results, meeting the needs of engineering design and quality verification.
Factors Affecting Aluminum Alloy Strength
|
Factors |
Key Elements | Impact on Strength |
|
Alloying Elements |
Mg, Si, Zn | Increase yield/tensile via precipitation or hardening |
| Processing Conditions | T6 heat treatment, H14 cold work |
Alters grain size, phase balance, and internal stress |
| Surface & Temperature | Porosity, cracks, and high service temperatures |
Lower effective strength, increase failure risk |
The mechanical strength of aluminum alloys is not only affected by chemical composition, but also depends on their processing and use.
Adding alloying elements such as magnesium and silicon can enhance hardness and strength, and T6 heat treatment significantly improves yield and tensile properties through microstructural adjustment.
Rough surface or high temperature environment may cause cracks or softening, significantly weakening the strength of the material.
Yield & Tensile Strength of Common Aluminum Alloys
|
Alloy |
Form | Temp | Yield Strength (MPa) | Tensile Strength (MPa) | Typical Applications |
|
Pure Aluminum |
Wrought | — | 20–30 | 30–90 | Foil, electrical, food-grade parts |
| 1050 / 1100 / 1200 | Wrought | O | ~25 | ~60 |
Chemical industry, architectural panels |
|
2004 / 2011 / 2014 / 2024 |
Wrought | T3/T4 | 200–320 | 300–470 | Aerospace, machined components |
| 3003 / 3004 / 3005 / 3105 | Wrought | H14 | 90–120 | 130–150 |
Cookware, HVAC, decorative panels |
|
4032 / 4045 |
Wrought | T6 | 150–170 | 240–300 | Automotive pistons |
| 5005 / 5052 / 5083 | Wrought | H32 | 150–285 | 200–330 |
Marine, building envelopes |
|
6061 / 6063 / 6082 |
Wrought | T6 | 214–276 | 240–310 | Automotive frames, fabrications |
| 7050 / 7075 / 7085 | Wrought | T6 | 400–503 | 475–572 |
High-performance aerospace parts |
|
8006 / 8011 |
Wrought | H19 | 110–135 | 160–200 | Packaging, foil structures |
| A206 / A213 / A319 | Cast | As-cast/T6 | 130–200 | 180–300 |
Engine blocks, housings |
|
A356 / A357 / AlSi7Mg |
Cast | T6 | 190–250 | 240–320 | Automotive wheels, pumps |
| A380 / A383 / A384 | Cast | As-cast | 120–150 | 180–240 |
Construction hardware |
|
A390 / A413 / A415 |
Cast | As-cast | 210–275 | 330–400 | High-stress engine parts |
| A440 / A443 / A444 | Cast | As-cast | 160–210 | 260–320 |
Transmission housings |
|
ADC10 / ADC12 |
Cast | T6 | 180–230 | 260–310 | Precision die-cast components |
| AlSiXMg (10/12/14/15/16/18) | Cast | As-cast | 140–200 | 220–300 |
Automotive, machinery castings |
| AlSi2Cu / AlSi5Cu3 / AlSi8Cu3 / AlSi9Cu3 | Cast | As-cast | 150–220 | 220–320 |
Valve bodies, pump housings, and lightweight parts |
Aluminum Alloy Selection Suggestions
Strength and Performance Balance
Aluminum alloy selection cannot only look at strength, but also needs to consider weldability, corrosion resistance, machinability, and cost.
For example, 5052-H32 is suitable for medium-strength applications in humid environments, while 6061-T6 is suitable for structural parts that take into account both strength and processing efficiency.
Actual Needs of the Industry
Automobile chassis and suspension systems require high-yield strength materials, such as 6061-T6, to prevent deformation caused by long-term loads.
Aviation structural parts use 7075-T6, emphasizing high tensile strength to prevent fracture.
Industrial castings such as pump housings and brackets need to take into account both strengths, and ADC12 or A356-T6 is commonly used.
CEX Casting: High-Strength Aluminum Alloy Die Casting Solutions
Structural Optimization and DFM Verification
All die-casting mold designs must be verified by flow and filling simulation before opening the mold to ensure reasonable filling and uniform cooling.
Combined with DFM design review and mold flow analysis, weak points such as shrinkage, cold shut, and bias flow can be discovered in advance, and the structural strength and consistency of die casting parts can be improved from the source.
Patented Squeeze Casting Process
Through the independently developed squeeze die casting process, the unique pouring and cooling control technology effectively reduces the internal pores and loose defects of die casting aluminum, improves the density of castings, and significantly enhances their yield strength and tensile strength.
CEX Squeeze Casting Process
Process Verification and Batch Testing
Each batch of aluminium die casting components undergoes tensile testing and hardness testing before leaving the factory to ensure that the yield strength and tensile strength are stable and meet the standards, eliminating performance fluctuations between batches.
We are equipped with our laboratory equipment to quickly respond to customer project needs.
Conclusion
Understanding yield strength and tensile strength is crucial for the selection of aluminum alloy materials.
Yield strength ensures shape stability, while tensile strength prevents the material from completely breaking.
Together, they define the load-bearing boundary of the structural design.
As a strength-focused aluminum die casting manufacturer, CEX Casting relies on patented casting technology and perfect quality control to ensure that each die casting product has stable and reliable mechanical properties.
Contact us today to get high-performance aluminum castings tailor-made for your next project.