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4000 Series Aluminum

The 4000 series is alloyed with silicon (5–13 %), which lowers the melting range without making the alloy brittle. Most of the family is not made into parts at all: it is the weld filler and brazing sheet used to join other aluminum grades. The exceptions are the forging grades, where silicon gives low thermal expansion and wear resistance for pistons, and the architectural grades that anodize to a dark gray.

Popular 4000 series grades

Compare in the explorer
GradeYield, MPaTensile, MPaDensity, g/cm³MachinabilityWeldabilityBest for
40431201802.68PoorExcellentGeneral-purpose TIG / MIG filler for 6000 series and castings
4047701702.66FairExcellentHigh-silicon filler and brazing alloy; less porosity
40323153802.69GoodFairForged pistons; low expansion, wear resistance
4045451102.67FairVery goodBrazing-sheet cladding for heat exchangers
41451102052.75FairFairFiller for 2000 series and Al-Cu castings
40061251452.7FairVery goodCasting and welding stock
4643701652.69FairExcellentHeat-treatable filler wire

All 27 4000 series grades

Choose the 4000 series for

Filler wire and rod for welding other aluminum (4043, 4047), clad brazing sheet (4045, 4343), forged pistons and other wear parts that see 150–200 °C (4032), and architectural extrusions that must anodize charcoal gray (4006, 4007).

Look elsewhere when

You want a machined or sheet-metal part — the 4000 series is a joining and forging family, not a general-purpose one. 6061 and 5052 cover almost every structural need; the silicon grades cost more and are rarely stocked in bar or plate.

Yield strength against elongation at break, 4000 series among every aluminum grade

No materials in view have both of these properties.

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4000 series by application

Welding aluminum
4043 for 6061, 6063 and cast alloys — fluid, crack-resistant, slightly gray after anodizing. 5356 (a 5000 series filler) where the joint will be anodized or the base is 5000 series.
Brazed heat exchangers
4045- and 4343-clad brazing sheet on a 3003 core: the clad melts at about 590 °C and joins fins to tubes in one furnace cycle.
Pistons and wear parts
4032-T6 forgings run hot with low thermal expansion and good wear resistance; 2618 is the alternative when higher strength matters more than expansion.
Dark architectural anodizing
4006 and 4007 anodize to a uniform charcoal gray without dye — curtain-wall and window extrusions.

Working with the 4000 series

As filler
4043 is the safe default for 6000 series and cast parts; it flows well and resists hot cracking but the weld anodizes darker than the base. Use 5356 when colour match after anodizing matters or the base is 5000 series.
Machining
Hypereutectic 4032 machines like a cast alloy — hard silicon particles abrade tools, so use carbide or PCD and moderate speeds. Finish is good and chips break short.
Forming
The silicon grades are not sheet alloys; forming is limited to the clad brazing sheet, which behaves like its 3003 core.
Finishing
High silicon anodizes gray to black and unevenly on cast-like surfaces — the reason 4006 / 4007 exist as deliberate dark-anodize grades and 4043 welds show on anodized parts.

Other aluminum series

4000 Series Aluminum — frequently asked

What is 4000 series aluminum?

The 4000 series is alloyed with silicon (5–13 %), which lowers the melting range without making the alloy brittle. Most of the family is not made into parts at all: it is the weld filler and brazing sheet used to join other aluminum grades. The exceptions are the forging grades, where silicon gives low thermal expansion and wear resistance for pistons, and the architectural grades that anodize to a dark gray.

Which grade of 4000 series aluminum should I use?

4043 is the general-purpose TIG and MIG filler for the 6000 series and cast alloys (5356 for the 5000 series); 4047 is the higher-silicon brazing and filler alloy. 4032-T6 is the forged-piston grade — low expansion, high wear resistance, strength to about 200 °C. 4006 and 4007 anodize charcoal gray for architectural cladding. Unless you are specifying a filler or a forged piston, the part you have in mind belongs in another series.

Which grade of 4000 series aluminum is the strongest?

4032 has the highest yield strength in the series at 315 MPa; 4006 follows at 125 MPa. Values are for each grade's default condition.

Which grade of 4000 series aluminum is easiest to machine?

ER4009 (machinability good, 60/100), then 4032 (55/100).

Is 4000 series aluminum heat-treatable?

Some grades are. Check the conditions listed on each grade page.

4043 or 5356 filler?

4043 (Al-Si) for 6000 series and castings: more fluid, less hot cracking, better for thick sections; it anodizes gray. 5356 (Al-Mg) for 5000 series and for joints that will be anodized or see salt water: stronger, better colour match, more ductile. Never use 5356 on parts that run above 65 °C for long — it sensitises to stress corrosion.

Why is 4032 used for pistons?

Its 11–13 % silicon gives about 15 % lower thermal expansion than 6061, so piston-to-bore clearance stays constant as the engine warms, and the hard silicon particles resist scuffing. T6 heat treatment gives it 300 MPa yield at room temperature and useful strength to about 200 °C.