For automotive powertrain castings running at 423-473 K (150-200°C), AE44 (Mg-4Al-4RE) and AS41 (Mg-4Al-1Si) are the two die-cast Mg workhorses most often lined up against each other on a drawing, and peer-reviewed creep data from the Monash group places them in clearly different performance tiers [S3].
AS41 has been the conventional elevated-temperature Mg alloy for decades, with its creep gain coming from the Mg2Si phase; AE44 is the newer Mg-Al-RE entry whose Al-RE intermetallics suppress the weak Mg17Al12 phase that kills AZ91 and AM60 above roughly 373-403 K (100-130°C) [S3][S4].
Alloy Chemistry and How Each Achieves Creep Resistance
AS41 is nominally Mg-4 wt% Al with about 1 wt% Si, where the Si forms Chinese-script Mg2Si skeletons in the eutectic that pin grain boundaries and slow dislocation climb at elevated temperature [S3]. AE44 is nominally Mg-4Al-4RE (a mixed rare-earth addition, typically Ce-La-Nd-rich mischmetal), which reacts with Al to form thermally stable Al11RE3 and Al2RE intermetallics instead of the low-melting Mg17Al12 [S1][S3].
The 2015 Monash comparative study covers AS31, AS41, AJ52, MRI153A, MRI153M, MRI230D, AXJ530, AE42, AE44, and AM-HP2+ side by side; the published creep-resistance ordering at 423 K (150°C) runs MRI230D > AM-HP2+ > AXJ530 > AE44 > AE42, with AS-family alloys trailing the AE and AXJ series on minimum creep rate at the same stress and temperature [S3]. Both alloy systems keep the Mg17Al12 phase from forming at the grain boundary, but the RE-bearing route preserves more ductility because the Al-RE intermetallics are less needle-like than the Mg2Si script morphology that can crack under cyclic load [S3][S4].
Strength, Ductility and Fatigue at 150-350°C
A 2026 SAE technical paper from General Motors (2026-01-0234) studies high-pressure die-cast AE44 from room temperature up to 350°C, and reports anelastic behaviour in both tensile and cyclic loading below 200°C tied to twinning, with that anelasticity vanishing above 200°C and giving conventional elastic-plus-plastic response [S5]. The paper proposes a 0.2% plastic-strain offset yield-strength method for HPDC AE44, which returns a higher σ0.2 than the traditional 0.2% total-strain offset commonly used for Mg [S5].
At room temperature, T5-aged Mn-bearing AE44 reaches a strength-ductility combination that the Monash group describes as better than most Mg die-casting alloys and even competitive with the Al die-casting benchmark A380, with the gain coming from nanoscale Al-Mn precipitates that form during direct ageing after casting [S2]. AS41, by contrast, is reported as having good room-temperature ductility but lower yield strength than A380, and the Mg2Si phase does not respond to T5 ageing the way the Al-Mn particles in AE44 do [S3]. For elevated-temperature yield strength, MRI230D, AXJ530 and AM-HP2+ in the same study exceed A380, while AE44 sits in the middle of the Mg pack and AS-family alloys anchor the lower end [S3].
Creep Test Results: 150°C and 175°C
The Zhu et al. metallurgical-transactions study ranks creep resistance of the commercial die-cast Mg alloys at 423 K and 448 K (150°C and 175°C); at 150°C, MRI230D, AXJ530, AE44 and AM-HP2+ are all reported as comparable to the A380 Al benchmark, with AS31 and AS41 trailing them in minimum creep rate [S3]. A separate 2010 study on AJ62 and AE44 confirms that both alloys hold good creep resistance at 175°C, with AE44 showing distinctly better creep behaviour than AJ62 in long-duration tests at that temperature [S8].
The 2021 Monash re-evaluation adds a nuance often missed in older datasheets: minor Mn is more important to AE44 creep resistance than the RE content itself, and the T5-aged Mn-bearing AE44 beats most Mg die-casting alloys on combined strength and ductility, which the authors flag as opening new automotive powertrain opportunities for the alloy [S1][S2]. For an engineer choosing between the two, the practical reading is that AE44 wins the 150-175°C creep ranking head-to-head against AS41, while AS41 remains a lower-cost, easier-to-source option where the service temperature stays at or below about 150°C and creep margin is not critical [S3][S4].
Process Considerations on a Die-Casting Cell
Both AE44 and AS41 are processed on conventional hot-chamber or cold-chamber die-casting machines, but the higher RE content of AE44 raises melt cost and slightly narrows the processing window, and the alloy is sensitive to Fe control so Mn is held in the melt to scavenge iron and keep corrosion behaviour in line [S1][S2]. AS41's Mg2Si script is a wear concern for the steel die-casting dies and trimming tooling, and the abrasive Si phase is one of the reasons AS41 has been partly displaced by Ca- and Sr-modified alloys in newer powertrain programmes [S3][S6].
For die-casting operations, lubricant suppliers note that newer Mg alloys with alkaline-earth or rare-earth additions are formulated to chase A380-class creep performance, and that RE-bearing melts need tighter release-agent and shot-sleeve management because of higher reactivity and different solidification ranges than AZ91 [S6]. The Monash characterisation of AE44 also underlines that the alloy is die-castability-friendly: it fills thin walls well and the T5 response means foundries can skip a solution treatment and go straight to artificial ageing after casting, which is unusual for an Mg die-casting alloy [S2].
Selection Criteria and Decision Matrix
The decision comes down to four engineering axes: operating temperature, required creep margin, ductility/fatigue demand, and cost. At 150°C continuous service, AS41 is acceptable for non-safety housings where minimum creep rate targets are modest, and it remains the cheaper, more available choice; at 175°C continuous service or where the part sees sustained stress at 150°C, AE44 is the safer pick because the Al-RE intermetallics stay thermally stable up to and beyond 200°C while Mg2Si begins to coarsen [S3][S8]. Forged-shape comparison context, including how RE-bearing and Si-bearing Mg alloys stack up against A380 Al, is detailed in the broader magnesium die-casting machine reference and the aluminum die-casting machine selection guide.
On ductility, both AS41 and AE44 outperform high-RE MRI230D and AXJ530 at room temperature, which matters for crash-loaded automotive structures, but AE44 additionally picks up T5 age-hardening from Al-Mn precipitation that AS41 cannot match, so AE44 is generally the higher-strength pick on a per-weight basis [S2][S3]. The Monash 2015 dataset also notes that AS31 and the AE series have very good room-temperature ductility while their yield strength is below A380, so any AE44 vs AS41 trade-off should weight yield strength and creep resistance together, not separately [S3]. A 2021 Brunel thesis on Mg-RE die-cast alloy development reinforces the AE44 positioning: Mg-4Al-4RE is described as a major achievement among Mg-Al die-casting alloys because it combines die-castability, room-temperature mechanical properties and high-temperature creep resistance in one system [S7].
Limits, Failure Modes and Sourcing
AE44 is not a universal answer: minimum creep rate at 150°C is still below the best MRI230D and AXJ530 grades, and Mn control must be maintained in the melt because Mn loss is tied directly to creep degradation, not just to corrosion rating [S1][S2]. AS41's failure mode at temperature is Mg2Si particle coarsening and eventual debonding from the α-Mg matrix, which sets a hard ceiling on its usable temperature near 150-175°C; going above that, the alloy creeps at a rate that designers do not accept for bolted powertrain components [S3]. Both alloys share the broader Mg die-casting limits: galvanic sensitivity to steel fasteners, need for surface protection in salt-spray service, and a flammable-melt safety protocol on the die-casting machine cell that is more stringent than for Al.
Sourcing signals to track: the SAE 2026-01-0234 paper from GM on HPDC AE44 tensile and fatigue behaviour up to 350°C was presented at WCX in Detroit on 2026-04-14, which is the kind of OEM dataset that tends to feed next-generation powertrain material specifications [S5]. The peer-reviewed creep ranking from the 2015 Monash paper (MRI230D > AM-HP2+ > AXJ530 > AE44 > AE42, with AS-family alloys below) has not been overturned by any 2024-2026 publication found in this research window, so it remains the working reference until a newer round of comparative data lands [S3].
Background reading: CBM vs PdM vs RCM: a decision matrix for plant maintenance.