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ZT68-600MPa Al-Mg High-Strength Bolt
I. Preface: Connection Technology Bottlenecks Under the NEV Lightweighting Wave
Driven by the dual-carbon policy and automotive energy consumption regulations, lightweighting has become the core development direction for new energy vehicles. According to the Energy-Saving and New Energy Vehicle Technology Roadmap 2.0 and the new GB 36980.1-2025 electricity consumption limit standards, vehicle weight reduction delivers clear quantitative benefits:
For NEVs, every 100kg weight reduction increases range by 6%–8%;
For ICE vehicles, every 100kg weight reduction lowers fuel consumption by 6%–8% and extends tire life by 7%;
Excise tax policies also favor lightweighting—for ICE vehicles, every 100kg weight reduction lowers the tax rate by 0.85%.
The lightweighting material evolution path is clear:
Vehicle bodies are transitioning from traditional single-material steel to multi-material composites including aluminum alloy, magnesium alloy, and carbon fiber. Chassis and three-electric system components are increasingly adopting magnesium alloy die-cast parts. Magnesium alloy is the lowest-density material among current engineering structural metals, with theoretical weight reduction of 30%–35%. Its application scenarios have expanded from dry-area interior small parts such as steering wheel frames and instrument panels to core three-electric wet-area components including battery trays and electric drive housings.
However, after large-scale deployment of magnesium alloys in vehicles, traditional steel fasteners have exposed two critical connection pain points:
Pain Point 1: Galvanic Corrosion Between Dissimilar Metals
Magnesium has an electrode potential as low as -1.6V, while ordinary carbon steel bolts have a potential of only -0.44V. The substantial potential difference forms a galvanic cell in humid environments, with the magnesium matrix acting as the anode and corroding rapidly, resulting in white rust, thread degradation, housing spalling, and leakage failures.
Pain Point 2: Preload Loss Caused by Thermal Expansion Coefficient Mismatch
Magnesium alloy has a thermal expansion coefficient of 26×10⁻⁶℃⁻¹, while ordinary steel has only 12×10⁻⁶℃⁻¹—a difference of more than double. Under vehicle thermal cycling conditions, the deformation mismatch between bolts and magnesium housings causes continuous preload loss over long-term use, leading to bolt loosening, seal failure, and structural noise.
The industry's current compromise solution is the 420MPa-class 6056 aluminum alloy bolt (AL9 Alu 6056). While it alleviates corrosion and thermal expansion issues to some extent, its strength ceiling is limited by cold-forging mass production constraints, making it incapable of meeting the high-torque, high-load connection requirements of three-electric structural components. This has become a core technological bottleneck hindering the implementation of magnesium alloy lightweighting.
Addressing this industry gap, Toprecision ZCJ, leveraging over 20 years of fastener R&D and manufacturing expertise, has independently developed the ZT68-600MPa cold-forged high-strength 7-series modified aluminum alloy bolt. This product breaks through the existing strength bottleneck of aluminum bolts, perfectly suits the connection needs of NEV magnesium alloy and aluminum alloy lightweight components, and provides a lightweight, highly reliable, long-life integrated fastening solution.
II. Corporate R&D and Manufacturing Capabilities
Toprecision ZCJ is an innovation-leading enterprise in China's fastener industry, with full industry-chain R&D, mass production, and quality inspection capabilities, providing solid support for ZT68 product commercialization:
Industry Layout: Shenzhen headquarters + Xiangyang automotive-dedicated production base + dual overseas factories in India and Indonesia, enabling global delivery; monthly fastener production of 500 million units, serving over 100 OEM and parts customers worldwide;
Certifications & Technological Accumulation: Obtained IATF16949 automotive industry quality certification in 2013, formally entered the NEV supply chain in 2017, and holds 26 effective fastener patents; in 2025, mastered the cold-forging process for ZT68 high-strength aluminum alloy bolts, with sample testing achieving tensile strength up to 630MPa and a nominal stable strength rating of 600MPa;
Full In-House Production: Self-established complete production lines including tooling development, multi-station cold forging, thread rolling, machining, heat treatment, surface treatment, automatic assembly, and optical sorting—no outsourcing required, with full quality control throughout;
Comprehensive Precision Testing Laboratory: Equipped with metallurgical microscopes, Brinell/Vickers hardness testers, 2D profile projectors, universal tensile testing machines, friction coefficient testers, spectrometers, constant temperature and humidity chambers, coating thickness gauges, ROHS detectors, and other full testing equipment. All mechanical, corrosion, and thermal stability tests can be completed in-house.
III. Performance Limitations of Mainstream Industry Aluminum Bolts
The current mainstream mass-produced aluminum alloy bolt in the industry is the 6056 (AL9 Alu 6056) 420MPa-class. Material parameters: EN AW 6056 (AlSi1MgCuMn), density 2.7 g/cm³, elastic modulus 69,000 MPa, linear thermal expansion coefficient 23×10⁻⁶℃⁻¹; lower yield strength limit 350MPa, tensile strength 400–440MPa, elongation after fracture ≥6%, maximum long-term service temperature 150°C.
Due to cold-forging mass production process limitations, this product has a low strength ceiling, and under high-load, thermal-cycling conditions in NEV three-electric systems, it suffers from insufficient load-bearing capacity—a long-standing pain point in industry lightweighting connections.
IV. ZT68 Core Technological Breakthroughs: Comprehensive Performance Upgrade Over 6056 Aluminum Bolts
1. Tensile Strength Test
ZT68 7-series modified vs. external hexagon flange bolt M8×40
Five parallel samples tested. Measured average maximum tensile force: 23,030.66N; average tensile strength: 629.25MPa; average yield strength: 510.20MPa; average elongation: 8.21%. Sample strength values were stable within 628–630MPa with minimal data scatter, demonstrating excellent batch-to-batch consistency.
Sample
Stress Cross-Sectional Area mm²
Max Force (Fbc) N
Tensile Strength (Rm) MPa
Yield Strength (Rp0.2) MPa
Yield Ratio
Elongation Af, %
Sample 1
36.6
22,997.92
628.36
524.2
0.83
8.29
Sample 2
36.6
23,046.27
629.68
521.57
0.83
8.02
Sample 3
36.6
23,020.37
628.97
502.59
0.80
8.22
Sample 4
36.6
23,060.81
630.08
498.26
0.79
8.22
Sample 5
36.6
23,027.95
629.18
504.37
0.80
8.31
Average
36.6
23,030.66
629.25
510.2
0.81
8.21
Performance Indicator
ZT68 600MPa-Class High-Strength Al Bolt
Industry Mainstream 6056 (AL9) 420MPa Al Bolt
Performance Improvement
Tensile Strength Rm
~630MPa
~420MPa
~ +50%
Yield Strength Rp0.2
~500MPa
~350MPa
~ +43%
Yield Ratio
~0.8
~0.85
Better ductility reserve
Elongation
≥8%
≥6%
Higher strength with maintained toughness
2. Head 6° Wedge Strength Limit Test
Simulating assembly impact and head load limit conditions. All 5 samples fractured in the unengaged thread section, with no head cracking or chipping. Cold-forged bonding strength between head and shank meets vehicle safety design standards. Sample ultimate tensile force range: 22.95KN–23.4KN, corresponding tensile strength 627MPa–639MPa.
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