Lightweight Design and Underbody Safety of New Energy Vehicle Battery Systems: Research Based on Aluminum Foam Structures

1.The New Standard Arrives: Traditional Chassis Guards Fall Short

In the past, many automakers cut corners on underbody protection for Battery packs to save costs and reduce vehicle weight—often doing just the bare minimum. However, once the new national standard (GB 38031-2025) is implemented, such shortcuts will no longer be viable.

 The new standard imposes two extremely rigorous requirements:

 150-Joule Bottom Impact: A steel impactor with a 30mm diameter strikes three high-risk points on the battery pack's underside with great force; the pack must show no leakage, fire, or explosion.

 35 km/h Underbody Scrape: A fully loaded vehicle scrapes directly over a solid iron hemisphere (150mm high) at a speed of 35 km/h; the vehicle must not catch fire or explode within two hours of the impact.

 This puts traditional steel and aluminum alloy plates in a difficult position:

 High-strength steel plates: Hard enough, but too heavy, significantly dragging down driving range.

 Standard aluminum alloy plates: Lightweight, but prone to tearing or puncture when subjected to sharp, localized impacts.

 This is where aluminum Foam—offering a perfect blend of rigidity and flexibility—emerges as the ideal choice. II. Aluminum Foam: A "Breathing" Metal Sponge

Simply put, aluminum foam is created by introducing countless tiny air pockets into pure aluminum or aluminum alloy, giving it the appearance of a metal sponge or honeycomb.

 The three-stage absorption mechanism of the product is the highlight. The three stages are:

In its elastic state, the product is similar to any metal - when a low energy impact is applied on it, it will absorb the energy and remain unchanged.

The yield plateau is the primary/critical stress point. The moment the force of impact becomes high enough, the bubbles of air trapped inside the material will collapse and fold one by one (like popcorn popping). While this happens, the material absorbs almost all the energy from the impact and provides a near constant reaction force.

Densification phase: Air voids are compacted completely so that the metal can become as solid as possible and gets the last solid support.

So if something like a rock or another thing sticking out hits the underside, then the aluminium foam will take all that sudden, localised, really high force by 'sacrificing itself' (having it's little air bubbles collapse), and there will be a very small amount of force that gets through to the battery cells.

it also combines with metal tubes or double layers of metal to form a composite material. This composite material is a result of the synergistic effect, known as the 1+1>2 principle, where the combination of the two materials is achieving more impact capacity than if they were developed independently. The aluminum foam serves as an internal structure to provide bracing for the outside metal shell; therefore, it does not break easily. It prevents the outside metal shell from breaking easily or locally. If you use this aluminum foam to fill the inner wall of the aluminum alloy tube, or fill the double-layer metal plate, the impact resistance of most composite structures can be doubled.

2.How is the "Armor" for the Battery Pack Bottom Designed?

In practical applications, engineers primarily use two mainstream approaches to "suit up" the battery pack in "bulletproof armor":

Option A: Aluminum Foam Sandwich (AFS) Panel

This is the most common approach. The structure resembles a sandwich: a top layer of high-strength aluminum alloy, a middle core of closed-cell aluminum foam, and a bottom layer of high-strength aluminum alloy.

How does it work? The outer panel resists sharp punctures from debris; the middle aluminum foam absorbs energy through significant deformation; and the inner panel ensures the battery cells are protected from crushing forces.

Advantages: It offers excellent large-area protection. Furthermore, because the closed-cell aluminum foam contains trapped air, it also serves as a highly effective thermal insulator. If a battery cell in the upper layer experiences thermal runaway (reaching temperatures above 120°C), this sandwich panel can withstand the heat for a full 900 seconds without transferring it to the layer below, buying precious time for firefighting and evacuation.

Option B: Biomimetic Aluminum Foam Block Arrays (ACCFBs)

What if the chassis space is too tight to accommodate even a flat panel? Scientists drew inspiration from human and animal skeletal structures to design a "discrete" protection system.

How does it work? Instead of using a single large sheet, the aluminum foam is cut into small square blocks (e.g., 125mm x 125mm), encased in small aluminum tubes, and distributed throughout the gaps in the chassis.

Advantages: It offers extremely high space utilization and allows for easy routing of wiring and cables. Furthermore, the gaps between the blocks facilitate heat dissipation for the battery pack during normal operation. Upon impact, the aluminum tubes constrain the foam blocks, enabling them to withstand massive loads—up to 25 times the battery's own weight.

3.Great Concept, but What Hurdles Remain for Mass Production?

Given the benefits of aluminum foam, why isn't it standard across all electric vehicle models? The main reason is that the industry has yet to fully overcome several recognized "tough challenges":

High Costs: Current manufacturing processes for aluminum foam are complex, and producing large, high-quality sheets is expensive; widespread use in consumer EVs (priced in the hundreds of thousands of yuan) places immense cost pressure on automakers.

Joining Processes Are Difficult. Aluminum foam has all kinds of holes. When you try to weld it (electric or laser), the heat melts the holes and they fall in, so there is no weld. Companies use expensive “vacuum brazing” or special glue systems to make things stick together. Both methods require strict standards during manufacturing.
Ageing Issues of Chassis Over Time:

The Chassis is constantly being exposed to wind, sunlight, mud, rain and exposure to corrosive salts. In the event the shell is breached, water penetrates the foam, and therefore, the electrochemical reaction will occur within the pores, resulting in a negative impact on the performance of your product due to a decrease in the amount of impact resistance over time.

Conclusion.
Safety should never be compromised at all. The era of "unprotected" new energy vehicle chassis has officially ended now that the new national standards are in place. As a material that reduces weight by more than 55% when compared to the steel used in crash components while providing multiple times the energy absorption of traditional steel, aluminum foam is not only one of the best materials available for the safe, lightweight design, but also offers the highest level of safety. With increasing maturity in production methods and reducing cost, "metal sponge" is on track to be manufactured in volume, providing greater peace of mind and confidence to all NEV owners in case of road debris or damage to the vehicle underbody.