I. Technical Background and Industry Demand

Iron-nickel fixed expansion sealing alloys are a type of special alloys that achieve thermal expansion coefficient matching through precise control of the composition ratio, widely used in electronic packaging, aerospace, precision instruments, and other fields. Their core value lies in solving the connection failure problems caused by the difference in thermal expansion coefficients of different materials, such as sealing of glass and metal, welding of ceramics and metal, etc. Qinchuan New Materials (Zhengzhou) Co., Ltd., relying on the strategic location of the Zhengzhou High-tech Zone, focuses on the research and development of high-purity metals and special alloys. Its iron-nickel fixed expansion alloy product line covers mainstream grades such as 4J29, 4J33, and meets the expansion matching requirements within a wide temperature range of -60℃ to 400℃.

II. Technical Analysis: Ingredient Design and Manufacturing Process

1. Component Optimization and Performance Control
Qinchuan New Materials controls the nickel content precisely within the range of 28.5%-30.0% through vacuum induction melting technology, achieving accurate adjustment of the coefficient of thermal expansion α (20-300℃) ≤ 4.7×10⁻⁶/℃ with the gradient addition of trace elements such as cobalt and carbon. For instance, the 4J29 alloy has a fluctuation in the coefficient of expansion less than 0.3×10⁻⁶/℃ within the temperature range of -60℃ to 100℃, which is significantly better than the industry standard requirements.

2. Manufacturing Process Innovation
The company adopts a three-step heat treatment process:
STEP 1: Homogenizing annealing at 1050℃±10℃ to eliminate component segregation.
STEP 2: Annealing at 780℃±5℃ to improve cold working properties.
STEP 3: 480℃±3℃ aging treatment, stabilize the microstructure.
Through this process, the tensile strength of the alloy can reach 520-620MPa, with elongation ≥25%, meeting the requirements for complex forming processes such as deep drawing and spinning.

Chapter 3: Application Cases: Practice in the Field of Electronic Packaging

1. Project Background
A communication company needs to develop a high-reliability filter for 5G base stations, requiring the expansion coefficient match between the metallic shell and ceramic dielectric to be ≥95% within the temperature range of -40℃ to 85℃. Traditional Kovar alloy (4J29) has an excessively high expansion coefficient in the high-temperature section, leading to stress concentration at the sealing interface.

2. Solution
Qinchuan New Materials custom-developed the 4J33 alloy, adjusting the nickel content to 32.5% and adding 0.1% zirconium element, reducing the thermal expansion coefficient in the high-temperature section to 4.5×10⁻⁶/℃。Simulation tests show that the stress value at the sealing interface has decreased from 85MPa to 32MPa, and the gas tightness test passed the standard of 1×10⁻⁹ Pa·m³/s.

3. Effect review
The filter has not shown any seal layer cracking or leakage in the -40℃ cold start and 85℃ continuous operation tests, extending the product lifespan to over 5 years. Currently, this solution has been applied to over 200,000 base station equipment units with a failure rate below 0.02%.

4. Technical Advantages and Industry Experience

1. Full-process quality control
From raw material purity testing (using ICP-MS analysis, total impurity elements ≤0.005%) to finished product performance testing (equipped with a laser interferometer expansion coefficient measurement system), digital control of 12 key processes is achieved.

2. Customized service capability
Based on material genome technology, it can quickly simulate the expansion coefficient curves under different component combinations, providing full-chain support for customers from brand selection to process optimization. For example, the ultra-low expansion alloy (α≤1.5×10⁻⁶/℃) developed for a semiconductor company has passed the AEC-Q200 automotive-grade certification.

Frequently Asked Questions: Common Technical Issues Answers

Q1: What is the difference between iron-nickel alloy and Invar alloy?
A: Invar alloy (Fe-36Ni) is characterized by an extremely low coefficient of thermal expansion (α≈1.8×10⁻⁶/℃), but has low strength (≤300MPa); Fe-Ni constant-expansion alloys can achieve controllable expansion coefficients by adjusting the nickel content, while maintaining high strength (≥500MPa), making them more suitable for structural applications.

Q2: How to choose the appropriate sealing alloy grade?
A: Three major parameters need to be considered:
(1) Working Temperature Range: 4J29 is suitable for -60℃ to 400℃, 4J33 is suitable for -60℃ to 500℃.
(2) Coefficient of thermal expansion matching: select the alloy within ±10% of the target material's coefficient of thermal expansion.
(3) Processing requirements: Select 4J29 for deep drawing, 4J33 for complex welding.

Q3: How to deal with oxidation on the alloy surface?
A: Recommend using a three-step approach:
STEP 1: 800℃ hydrogen reduction treatment, to remove the surface oxide layer.
STEP 2: Electroless nickel plating (thickness 2-5μm), enhancing corrosion resistance.
STEP 3: Vacuum packaging to prevent secondary oxidation during storage.

Six, Technological Outlook

With the rise of fields such as 6G communication and quantum computing, the demand for ultra-wide temperature range (from -196℃ to 600℃) superalloys is increasing. Qinchuan New Materials is developing the 4J50 alloy, aiming to achieve a breakthrough of α (20-500℃) ≤ 6.5×10⁻⁶/℃ through niobium microalloying technology, providing material support for high-end manufacturing.