Riveted Assembly With Metallurgical Bonding for Dissimilar Materials
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Solution Overview
Problem
Conventional welding and riveting techniques face challenges in joining dissimilar materials like magnesium and aluminum alloys with other metals or carbon fiber composites due to differences in physical and mechanical properties, leading to brittle intermetallic compounds and poor metallurgical bonding, which can result in interfacial fracture and corrosion issues.
Innovation Solution
The use of rotational hammer riveting (RHR) technique generates heat and pressure to create a metallurgical bond between a rivet stop head and metal-comprising substrates, such as magnesium or aluminum sheets, forming a mixed interface that seals against corrosive electrolyte penetration and improves the formability of tempered alloys.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional welding techniques are used to join dissimilar materials like magnesium and aluminum alloys, then joining strength can be achieved, but brittle intermetallic compounds form at the interface leading to interfacial fracture
Solution Approach 1:
A transition layer or intermediate material is introduced between dissimilar metal substrates (e.g., aluminum and magnesium) to prevent direct contact and intermetallic compound formation. This intermediary layer acts as a buffer that maintains metallurgical bonding while preventing the formation of brittle intermetallics at the interface, thereby improving joint reliability without sacrificing strength.
Solution Approach 2:
The chemical composition, thickness, or microstructure of the transition layer is optimized to control the bonding interface properties. By adjusting parameters such as layer composition (e.g., aluminum alloy composition), thickness, or thermal treatment, the system achieves strong metallurgical bonding while preventing harmful intermetallic formation, resolving the contradiction between strength and reliability.
2Ease of manufacture
If conventional riveting is used to join materials, then assembly can be achieved, but no metallurgical bond is formed leading to poor sealing and compliance under shock and vibration
Solution Approach 1:
The conventional purely mechanical riveting system is replaced or enhanced with a thermomechanical process. The rivet is heated to elevated temperature and then impacted into the substrate, creating a metallurgical bond through diffusion and intermetallic formation controlled conditions. This substitutes the simple mechanical insertion process with a thermally-assisted process that achieves both ease of manufacture and reliable metallurgical bonding.
Solution Approach 2:
The rivet material undergoes phase transitions during the joining process - heating the rivet to austenite phase, then rapid cooling during impact causes martensitic transformation. This phase transition enables the rivet to be soft during insertion (ease of manufacture) and then harden to provide strong metallurgical bonding and shock resistance (reliability).
3Strength
If tempered 2XXX and 7XXX Al alloys are riveted at room temperature, then strength is maintained, but low formability prevents deformation during impact riveting
Solution Approach 1:
The temperature parameter of the riveting process is changed from room temperature to elevated temperature. Heating the tempered aluminum alloys (2XXX or 7XXX series) to temperatures above their recrystallization point temporarily restores ductility and formability, allowing the material to deform during impact riveting while maintaining its high strength properties after cooling.
Solution Approach 2:
The rivet or workpiece is preheated to elevated temperature before the impact riveting operation. This preliminary thermal treatment puts the material in a soft, formable state before deformation occurs, allowing the tempered high-strength alloy to be shaped during riveting. After cooling, the material retains both the formed shape and its high strength properties.
4Ease of manufacture
If 7XXX Al alloys are hot riveted, then formability is improved, but strength dramatically decreases due to second phase coarsening
Solution Approach 1:
The riveting process uses dynamic, high-strain-rate impact loading rather than slow, static deformation. This dynamic loading method enables formability at lower temperatures by utilizing strain-rate sensitivity of the material, avoiding the need for prolonged high-temperature exposure that would cause second phase coarsening and strength loss. The rapid deformation occurs before significant diffusion or coarsening can take place.
Solution Approach 2:
Instead of changing temperature to improve formability (which causes strength loss), the strain rate parameter is changed. High-strain-rate impact riveting at or near room temperature exploits the material's strain-rate sensitivity to achieve formability without thermal exposure, thereby maintaining the high strength of 7XXX alloys by preventing second phase coarsening.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
RHR enables strong, flexible multi-material assemblies with increased riveting speed, overcoming the limitations of conventional methods by forming a metallurgical bond that enhances mechanical properties and reduces the risk of interfacial fracture, particularly for alloys like 2024 and 7075 Al and Mg alloys, which were previously difficult to rivet at room temperature.
Implementation Method 1
The use of rotational hammer riveting (RHR) technique generates heat and pressure to create a metallurgical bond between a rivet stop head and metal-comprising substrates
Implementation Method 2
The use of rotational hammer riveting (RHR) technique generates heat and pressure to create a metallurgical bond between a rivet stop head and metal-comprising substrates
Data Source
AI summary
Riveted assemblies are provided that can include a substrate extending between two ends to define opposing substrate surfaces having a first opening extending between the opposing substrate surfaces; a metal-comprising substrate extending between two ends to define opposing metal-comprising substrate surfaces having a second opening extending between the opposing metal-comprising substrate surfaces. The riveted assemblies can further provide that the first and second openings complement one another when the substrate and metal-comprising substrate are engaged; and a rivet shaft extends through the openings and engages the substrate with the rivet head and the metal-comprising substrate with the rivet stop head, at least a portion of the stop head being mixed with, and forming a metallurgical bond with the metal-comprising substrate. Assemblies are provided that can include a rivet stop head mixed with, and metallurgically bonded with a metal-comprising substrate.Methods for affixing substrates to one another are also provided. The methods can include providing a substrate defining an opening configured to receive a rivet shaft; providing a metal-comprising substrate defining a complimentary opening; operatively engaging the substrates with the rivet shaft; and forming a stop head from the rivet shaft to affix the substrates. The method further includes that the stop head mixes with, and forms a metallurgical bond with the metal-comprising substrate. Methods for mixing materials to form a metallurgical bond are also provided. The methods can include forming a metallurgical bond between a stop head of a rivet and a metal-comprising substrate.