A380 and A356 are quoted on separate Platts secondary-alloy price tracks because their chemistry, process fit, and total cost of ownership are not interchangeable, and the spread between the two tracks is set by copper content, heat treatment, and volume tier [S6].
A380 is a high-pressure die-casting Al-Si-Cu alloy with 7.5-9.5% Si and 3.0-4.0% Cu, while A356 is a heat-treatable Al-Si-Mg gravity casting alloy with 6.5-7.5% Si and 0.25-0.45% Mg; A356 is the most common gravity casting alloy cast in North America and A380 is the most common aluminum die casting alloy in the same market [S1][S2]. The full cost comparison therefore starts with alloying content, runs through process and temper, and ends at the piece-price or per-part cost that an OEM actually pays.
What moves A380 and A356 prices apart
Alloying additions are the largest chemistry-driven cost delta. A380 carries 3.0-4.0% Cu versus A356's ceiling of 0.20% Cu, and copper is the most expensive common alloying element in aluminum casting [S1]. A356 trades copper for magnesium (0.25-0.45%) and lets heat treatment do the work, which means a lower alloying-billet cost but a real T6 processing line item.
Process fit shapes the second cost layer. A380 is a high-pressure die-casting alloy with a melting range of roughly 540-595 °C that fills thin walls efficiently, while A356 is cast at around 570-610 °C in sand or permanent-mold routes, with an A356-T6 tensile strength of about 270 MPa compared to about 324 MPa for typical A380 die castings [S1][S5]. HPDC cycle time on A380 is in seconds; sand or permanent-mold A356 cycle time is in minutes, and that takt differential feeds directly into the per-part price [S3].
For sourcing teams comparing China factory options, this is also a capability question rather than just a material one, since not every Chinese die-casting shop runs low-pressure or gravity A356 cells on the same floor as HPDC A380 [S3].
Composition and property ranges that hit the invoice
The chemistry windows drive both price and behavior, and a buyer should know the band before negotiating a quote. The Silicon range in A380 (7.5-9.5%) sits higher than in A356 (6.5-7.5%), which improves fluidity and reduces hot tearing in HPDC; A356's lower Si and tight Mg window (0.25-0.45%) is what unlocks the T6 response that structural casters need [S1][S4].
Physical property deltas that affect downstream cost are real but small: A356's thermal conductivity is roughly 150 W/m·K versus about 96-113 W/m·K for A380, A356 density sits near 2.6-2.68 g/cm³ versus about 2.71 g/cm³ for A380, and elastic modulus is in the 70-72 GPa range for both [S1]. A slightly heavier A380 part is one more weight-driven cost variable on shipping, and the thermal-conductivity gap matters when the casting is a heat-dissipation housing versus a structural bracket.
Iron is the silent price lever. Standard 356 allows more iron than the tighter A356 specification, and that higher iron lowers ductility and elongation; for safety-critical structural castings, A356's lower iron ceiling is what buyers pay a premium for, not just the tighter chemistry paperwork [S4].
Process and total cost of ownership comparison
Three decision criteria line the two alloys up cleanly: per-kg billet cost, in-process cost, and post-process cost. A380 wins on per-kg billet cost at very high volume and minimal finishing, A356 wins on per-kg billet cost at lower volume with structural performance needs, and the total-cost winner depends on whether the part needs T6 temper, weldability, or corrosion performance [S1][S2][S5].
Post-process cost is where A356 catches up. A356 is weldable and heat-treatable to T5 and T6 conditions, which is why it dominates in automotive structural, robotic, and load-bearing applications; that weldability and heat-treatability come at the price of a T6 line, but the line is well-understood across North American and Chinese gravity foundries [S2][S4]. A380 is essentially a finished as-cast part: it cannot be meaningfully heat-treated, so post-process cost is mostly limited to trim, shot blast, and any machining, which keeps A380's TCO competitive at high volume [S1].
Corrosion performance is a TCO line item. A380's 3.0-4.0% Cu reduces corrosion resistance relative to lower-copper aluminum casting alloys, and A356's lower Cu ceiling plus Mg-based protection makes it a more common pick in marine, agricultural, and outdoor structural service [S1][S4][S7]. For a buyer running a 10-year service life, the coating or anodizing step on an A380 part versus the as-cast or conversion-coated A356 part is a measurable lifetime cost.
Market and benchmark pricing references
Platts publishes a US A380 secondary aluminum alloy price alongside five other secondary aluminum alloy prices suitable for diecasting or foundry applications, and that A380 assessment is the de facto US benchmark for high-pressure die-casting alloy [S6]. Secondary-alloy pricing is the right benchmark for A380 because most A380 in North America runs on secondary (recycled) feedstock, and the secondary track moves on scrap spreads, not just LME primary aluminum [S6].
For A356, secondary gravity casting alloy tracks generally follow the same Platts and Fastmarkets family of benchmarks, with price points below A380 on a per-kg basis because the Cu content is roughly an order of magnitude lower. North American volume data is explicit: A380 is the most common aluminum die casting alloy in North America, A356 is the most common gravity casting alloy cast in North America, and that volume split is why both keep separate benchmark lines [S2].
China sourcing adds a regional layer. Chinese suppliers will quote A380 HPDC and A356 low-pressure / gravity on the same RFQ, but the cell layout, furnace fleet, and heat-treatment line at the supplier need to be matched to the alloy and process specified, otherwise the cheaper-sounding A356 quote can hide missing T6 capacity or limited low-pressure cells [S3].
Selection rules for buyers and specifiers
Pick A380 when the part is a high-volume die casting with thin walls, complex geometry, and as-cast performance is acceptable; A380 is also the safer pick for die-cast aluminum alloy projects where the entire part is shot in a single HPDC cycle and the buyer wants minimal finishing [S1][S2][S7]. Pick A356 when the part is a structural or safety-critical gravity casting that will be welded, heat-treated to T6, or run in a corrosive outdoor environment, including pumps, housings, brackets, agricultural components, marine parts, EV structural components, robotics, and medical device components [S2][S4].
Pick the standard 356 grade (not A356) when cost is the primary driver, ductility and elongation margins are wider, and the iron ceiling is acceptable for the application; pick A356 when the part must carry load, resist cracking under impact, and meet tighter chemistry limits [S4]. A380 is a poor choice for any welded assembly or T6 temper requirement, and A356 is a poor choice for thin-wall HPDC where cycle time matters more than post-cast strength.
For corrosion-heavy service, A383 (a higher-Si, lower-Cu variant of A380) is often a better die-casting pick than A380 itself, with slightly improved corrosion resistance, hot-cracking resistance, fluidity, and elevated-temperature strength compared to A380 [S2]. A356.0 (the strict-tolerance variant) is the structural equivalent of A383's role in the HPDC world.
Limitations and failure modes to flag in the RFQ
A380 fails predictably in three modes: corrosion-driven service life loss in marine or de-icing-salt environments, hot tearing when Cu and Fe push too high, and cracking under post-cast welding because the Cu-rich matrix cannot tolerate weld thermal cycles [S1][S7]. A356 fails predictably in three different modes: porosity and shrinkage in heavy-section sand castings without proper risering, brittle fracture when iron drifts above spec, and dimensional instability after T6 if the quench rate is not uniform [S1][S4].
For more on the cell equipment side of the A380 HPDC decision, the equipment stack from press to auxiliary drives a large fraction of piece-price, and is mapped spec-by-spec in the related HPDC cell equipment list coverage. For the A356 gravity side, the ladle-to-pour window of 20-50 °C superheat is one of the cheapest defect controls a foundry can run, and the principles are walked through in the ladle preheat and superheat window reference. Sand-system and reclamation quality in 2026 is a separate but linked cost variable, and the foundry sand reclamation automation coverage maps what to ask a supplier to prove on the line.
Standards and sourcing due diligence
Both alloys sit under the broader Aluminum Association designation system: A356.0 for the strict-tolerance structural variant, 356.0 for the standard variant, and A380.0 for the high-pressure die-casting grade. Buyers should confirm the actual registration on the mill cert and not rely on the colloquial grade name, since A356 vs 356 is exactly the chemistry-control question Precision Enterprises and other foundries are calling out [S4]. For die-cast corrosive service, ADC12 is the JIS equivalent most Chinese and Japanese die-casting shops will quote alongside A380, and the trade-offs between A380, A356, and ADC12 for corrosive service are laid out in the Kenwalt guide [S7].
Trackable next signals for Q4 2026 sourcing: the Platts US A380 secondary aluminum alloy assessment and its five companion secondary tracks will be the cleanest read on whether A380 billet pressure is moving on scrap spreads or on Cu alloying cost [S6]; Chinese gravity-casting capacity for A356-T6 in Ningbo and the Pearl River Delta will set the global A356 lead-time band, and shop-level low-pressure cell counts are a more useful signal than headline foundry counts [S3].
Component reference pages worth checking: aluminum die casting machine, aluminum alloy, and construction machinery and equipment.