Case Study: 150W LED Streetlight Housing -Thermal and Coastal Durability

Customer: LED lighting OEM, Netherlands Program: 150W streetlight housing for municipal coastal installation Annual volume: 35,000 pieces/year Material: A360 aluminum + e-coat + powder coat Weight: 2.1 kg Requirements: Thermal resistance <0.12°C/W, IP66, 10-year coastal service life (800-hour salt spray minimum)

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The Challenge

Previous design: A380 aluminum with direct powder coat. Failing their 800-hour salt spray qualification when tested after 2-year accelerated cyclic corrosion simulation. Coating intact -but underlying aluminum showed pitting at fin edges through coating micro-cracks.

Simultaneously, LED junction temperatures at 84°C in 35°C ambient -1°C below the 85°C limit with no margin for production variation or LED aging.

Two problems, one program.

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Solution

Alloy Change: A380 →A360

A360's copper content (0.6% max vs A380's 3.5%) eliminates the galvanic corrosion mechanism driving pitting. Comparative salt spray: A380 without coating showed pitting at 120 hours; A360 without coating showed none at 500 hours.

Coating Change: Direct Powder →E-coat Primer + Powder

E-coat (cathodic epoxy, 18 μm) applied before 70 μm powder topcoat. E-coat provides full coverage on fin inner faces and internal surfaces inaccessible to spray powder -a continuous barrier layer that protects the substrate even if the topcoat is scratched during installation. Combined result: >1,200 hours salt spray, 150% of specification.

Fin Geometry Correction

DFM review found 6 of 18 fins exceeding 4:1 height-to-thickness castability ratio -causing inconsistent fill (3 fins short-filling on 12% of shots). Revised to maintain fin height while increasing thickness from 1.5 mm to 1.8 mm.

Thermal improvement: More uniform fin fill + A360's higher thermal conductivity (113 vs 96 W/m·K for A380) dropped LED junction temperature from 84°C to 78°C -a 6°C improvement creating adequate margin.

IP66 Sealing

O-ring groove geometry re-specified to match AS568 O-ring standard sizes. Surface finish Ra <1.6 μm on groove radius. First-article IP66 test (20 kPa water jet, 3 minutes): 12/12 pass.

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Results

Metric	Previous (A380)	KastMfg (A360)
Salt spray	480 hrs (fails 800 hr spec)	>1,200 hrs
LED junction temp at 35°C	84°C	78°C
Fin fill consistency	88%	100%
IP66 first-article pass	8/12	12/12
Coating adhesion (cross-hatch)	GT2	GT0

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Contact KastMfg: yaoqingpu1983@gmail.com | +86 138 1403 4409 | No.6, Rungu Road, Nanjing, China