Thread & Panel
Lightweight joints without galvanic corrosion
Lightweight joints · Thread & Panel Overview
When a steel bolt is fastened into a magnesium or aluminium housing, two problems appear at once. The first is electrochemical: steel, aluminium and magnesium sit far apart in the galvanic series, so the joint becomes a corrosion cell and the lightweight base metal is the part that is consumed. The second is thermal: the steel and the light alloy expand at different rates, so a hot joint loses preload as the temperature rises.
An aluminium bolt addresses both at the source. Because it is metallurgically close to the magnesium and aluminium parts it is clamping, the galvanic driving force is very low, so no isolating washer or sacrificial coating is needed. And because its thermal expansion matches the housing, preload is retained at operating temperature. The result is a lighter joint that stays tight — which is why this is one of the few areas where aluminium has displaced steel in structural fastening.
Material
7-series high-strength aluminium alloy (ZT68 grade)
Average tensile strength
629.25 MPa (5-coupon average, tested at 5 mm/min)
Average yield strength
510.20 MPa (Rp0.2)
Elongation after fracture
8.21% average
Yield-to-tensile ratio
0.81 average
Weight saving vs steel
Up to 65%
Design intent
Six engineering decisions that separate a micro fastener that works from one that merely fits the drawing.
Five test coupons averaged 629.25 MPa tensile and 510.20 MPa yield, with 8.21% elongation and a yield ratio of 0.81 — strength and ductility balanced.
Steel is roughly three times the density of aluminium, so replacing a steel bolt with an aluminium one removes up to 65% of the fastener mass.
Because the bolt and the light alloy housing sit close together in the galvanic series, the corrosion driving force is very low and no isolating barrier is required.
A steel bolt in the same joint loses more than 96% of preload at 150 °C; the aluminium bolt loses 40–55%, because its expansion matches the housing.
Cold forming produces the flange as part of the bolt, so bolt and washer become one part — removing the separate washer, its inventory and the risk of it being displaced.
Rolling after ageing puts uniform residual compressive stress into the thread root, which offsets service tensile stress and raises fatigue strength.
Technical data
Reference data for design and sourcing. For a specific part, the drawing governs — these tables are the starting point for a joint review.
| Coupon | Area (mm²) | Max force (N) | Tensile Rm (MPa) | Yield Rp0.2 (MPa) | Elongation Af (%) |
|---|---|---|---|---|---|
| 1 | 36.6 | 22,997.92 | 628.36 | 524.20 | 8.29 |
| 2 | 36.6 | 23,046.27 | 629.68 | 521.57 | 8.02 |
| 3 | 36.6 | 23,020.37 | 628.97 | 502.59 | 8.22 |
| 4 | 36.6 | 23,060.81 | 630.08 | 498.26 | 8.22 |
| 5 | 36.6 | 23,027.95 | 629.18 | 504.37 | 8.31 |
| Average | 36.60 | 23,030.66 | 629.25 | 510.20 | 8.21 |
Values are typical for the stated material and finish. Actual performance depends on the mating material, engagement length and assembly torque. Confirm with a sample test before design freeze.
Options
Mix these within one part number family. Where a combination is not manufacturable at your tolerance, we will say so at quotation rather than after the first lot.
Where it is used
Representative positions rather than an exhaustive list. Many of our parts are designed for one specific assembly and never appear in a catalogue.
| Assembly | Typical use |
|---|---|
| Transmission housing | Bolting an aluminium or magnesium housing without a galvanic couple |
| Battery pack frame | Lightweight structural joints in an aluminium frame |
| Motor and inverter mount | Bolts retaining a housing at sustained operating temperature |
| Chassis node | Weight reduction at a multi-bolt joint where every gram counts |
| Magnesium die-casting | Threaded joint to a magnesium part without isolation washers |
| Weight-critical assembly | Replacing steel fasteners where fastener mass is a significant share |
Quality control
Inspection is not a final gate. It is a set of checks placed where a process can actually drift, with the result recorded against the lot code.
01
Tensile test to the specified rate, coupon basis
02
Yield strength and elongation, per test report
03
Wedge load and proof load where specified
04
Metallographic structure after heat treatment
05
Thread gauge after thread rolling
06
Coating thickness and friction coefficient control
07
Neutral salt spray and galvanic corrosion testing
08
Full dimensional and appearance inspection before packing
Questions
The questions our engineers answer most often on this product family.
Related products
These families are frequently used in the same assembly, or as an alternative when the joint requirement changes.
Thread & Panel · Light alloy & plastic
Thread inserts give a lightweight structure a thread that survives repeated assembly — wire thread inserts, self-tapping inserts and key-locking inserts for plastic, aluminium and magnesium.
Micro Screws · M0.6 – M2
Micro machine screws that engage a pre-formed thread — a tapped hole, a brass insert or a heat-set nut — and hold their clamp load through repeated disassembly.
Thread & Panel · Joint anti-loosening
Lock washers are among the core anti-loosening fasteners for robot joints and transmission systems, holding preload where vibration would otherwise relax the joint.
Send a drawing or 3D model with the mating material and finish requirement. The reply is a process route, a tolerance review and a price — with the assumptions stated.
