Overview
MIC-6 is a precision-cast aluminum tool plate designed for one job: stay flat after heavy machining. The cast granular structure, combined with in-line stress relief during the continuous-casting process, eliminates the residual stress that causes wrought aluminum plate to warp during machining of deep pockets, thin walls, and large flat surfaces.
What MIC-6 does:
- Stays flat. ±0.005″ flatness on 1/4–4″ thick plate, maintained after heavy stock removal. This is the entire reason MIC-6 exists.
- Machines easily. Forgiving on tool selection, short broken chips, predictable surface finish.
- Stable thermal cycling up to ~425°C per manufacturer data.
- Ships ready-to-use — precision-ground both sides, PVC film protected, dimensional tolerance ±0.005″ on thickness.
What MIC-6 doesn’t do:
- Structural strength — 15 ksi yield. MIC-6 is for tooling, not load-bearing parts.
- Welding — cracks and porosity during fusion welding. Design for mechanical fastening.
- Forming — 3% elongation. Not bendable.
- Decorative anodize — cast porosity produces dark spots in the finish.
- Fatigue service — cast structure has lower fatigue strength than wrought.
The selection logic is simple: if your tooling plate will be heavily machined and must stay flat, MIC-6. If you need structural strength, mechanical load capacity, or weldability, 6061-T651 plate is the right starting material.
Why cast aluminum stays flat
Wrought aluminum plate is rolled from larger ingots. The rolling process introduces residual stress that doesn’t fully relieve during mill annealing. When a wrought plate is heavily machined:
- Removing material from one side changes the stress balance
- Residual stress redistributes to a new equilibrium
- The plate bows to accommodate the new stress state
- Tight tolerances are lost — fixture plates with ±0.001″ flatness become ±0.005″ or worse after machining
The wrought-aluminum solution is T651 stretch relief — stretch the plate after solution treatment to relieve residual stress before final aging. 6061-T651 and 7075-T651 plate are designed for exactly this issue, and they work — but stretch-relieved plate still has some residual stress, and very heavy machining can still cause warpage.
MIC-6 takes a different approach. Cast aluminum plate is solidified in place from molten metal. The continuous-casting process produces a fine granular structure without the directional stress of rolling. Combined with in-line stress relief (the casting line includes a controlled cooling section), the resulting plate has essentially zero residual stress to release during machining.
The result: machine away. Deep pockets, thin walls, full one-side pockets — the MIC-6 plate stays within ±0.005″ flatness regardless of how much material is removed. This is the property that makes MIC-6 the canonical tooling plate.
Machining notes
MIC-6 is one of the most forgiving materials to machine:
- Carbide or HSS — both work well
- Speed: 600–2000 SFM
- Feed: 0.005–0.025 in/rev
- Cutting fluid: optional for light passes, recommended for heavy stock removal
- Tool life: excellent (non-abrasive)
Chip behavior is the standout feature — cast aluminum forms short broken chips that clear gravitationally. Chip control problems that plague 6061 are nonexistent on MIC-6. Unattended multi-hour machining runs are routine.
Surface finish caveat — the cast granular structure produces microscopic porosity visible at high magnification. 32 Ra surface finishes are routine; 16 Ra achievable with finishing passes; but mirror finishes (8 Ra and below) are not achievable due to the cast porosity. For optical-quality flatness with mirror finish, use wrought 6061-T651 ground to flatness.
Pocket and thin-wall machining is where MIC-6 shines. Deep pockets (10× depth-to-width), thin walls (~1 mm), full one-side machining — all routine without distortion concerns. The cost premium over 6061-T651 plate pays back quickly in eliminated rework.
Applications
The dominant MIC-6 applications all share the same requirement: flat plate that must stay flat after machining.
- CNC mill and lathe fixtures — the canonical application. Custom workholding plates machined to mounting hole patterns, vacuum slots, dowel locations. MIC-6 holds flatness through the machining and maintains it in service.
- Vacuum tables for CNC routers, laser cutters, and waterjet machines. Drilled with vacuum grids; sealed surface. Hard anodize for wear durability.
- Jig plates and gauge plates — inspection fixtures, measurement jigs, drill templates. Flatness is the primary spec.
- Mold base plates for plastic injection molding (short-run and prototype tooling), thermoforming, and vacuum forming. The cast porosity is acceptable on mold base plates; the actual mold cavity is typically a hardened tool steel insert.
- Robotic end-effector mounting plates — flatness ensures predictable robot kinematics.
- Optical breadboards (entry-level) — for high-precision optical benches, machined-grid 6061-T651 or commercial optical breadboards (Newport, Thorlabs) are preferred; MIC-6 is the budget alternative for less-demanding applications.
- Electronics assembly fixtures — PCB hold-downs, component placement jigs, soldering fixtures.
- 3D printer build plates (selected) — flatness for FDM and SLA build platforms; some printer manufacturers use MIC-6 plates, others prefer wrought 6061 with anodize.
Welding and joining
Don’t weld MIC-6 for structural service. The cast structure with fine porosity produces:
- Severe weld porosity — entrapped gas in the cast structure vents into the weld pool
- Hot cracking at the weld and HAZ
- Strength loss in the weld zone (already starting at 15 ksi yield — the weld is weaker still)
Design MIC-6 tooling for mechanical fastening:
- Machined threaded holes (helical inserts or solid threads) for bolts
- Dowel pins for repeatable positioning
- Bolted assemblies with shoulder bolts for shear loading
- Adhesive bonding for non-structural connections
If a tooling plate must be welded as part of a larger assembly, switch to wrought 6061 for the weldable section and bolt the MIC-6 plate to it.
Surface finishes and protection
- Bare MIC-6 — Indoor service essentially permanent. The natural oxide protects against the typical machine-shop environment (coolants, occasional water, oil, atmospheric humidity).
- Hard anodize (Type III) — Used on vacuum tables and wear-prone fixtures. Significant durability improvement; cosmetic non-uniformity irrelevant.
- Type II anodize — Functional corrosion protection. Cosmetic pinpoint spots at cast porosity sites; acceptable for industrial fixtures, not for display.
- Chromate conversion — Paint primer for outdoor-stored fixtures or display tooling.
- Powder coat — Decorative finish for consumer-facing fixtures and display equipment. Hides the cast texture and matte finish.
Failure modes worth designing around
Using MIC-6 as a structural plate is the #1 designer error. The low yield strength (15 ksi) is inadequate for any meaningful structural load. For load-bearing applications, use 6061-T651 (40 ksi yield) and machine for flatness with proper rough/finish sequencing.
Attempting to weld MIC-6 in field repair is the second common error. The cast structure cracks and produces porous welds. Design mechanical fastening from the start; for field repair, mechanical patches over the damaged area.
Attempting to bend or form MIC-6 — 3% elongation means any bending operation cracks the plate. Cast aluminum is not formable; design tooling as machined-from-plate parts.
Anodizing for cosmetics — cast porosity produces dark spots in the anodize finish. Don’t specify decorative anodize on MIC-6. For visible-quality anodize on tooling, use wrought 6061 (lighter cosmetic anodize) or 6063 (best anodize uniformity).
Fatigue service — cast structure has lower fatigue strength than wrought. MIC-6 is not appropriate for fatigue-loaded service (rotating equipment, vibration-loaded fixtures). For fatigue applications, use wrought 6061 or 7075.
Cost-inefficient use for non-flatness-critical parts — MIC-6 costs ~50% more than 6061-T651 plate. For tooling that won’t be heavily machined, or where T651 stretch relief is adequate, 6061-T651 is the cost-effective choice. Use MIC-6 specifically for parts requiring flat surfaces after heavy machining.
Thermal expansion mismatch with steel fixtures — at 23.6 ppm/°C versus ~12 ppm/°C for steel, MIC-6 plates bolted to steel bases expand twice as much per degree. For temperature-cycled tooling (thermoforming, low-temperature molds), this can cause fastener fatigue or warpage. Use slotted holes or floating connections to allow differential expansion.